Li cm n
Kha lun tt nghip ny c hon thnh di s ging dy v hng dn trc tip ca
GS.TS Nguyn Nng nh. Vi s knh trng v lng bit n su sc, em xin chn
thnh cm n gio s v s hng dn tn tnh trong thi gian thc hin kha lun.
Hn na, trong sut nhiu nm hc ti khoa Vt l k thut v Cng ngh nano, thy
lun ging gii, truyn t cho em nhng kin thc b ch, dy cho chng em cch
t duy khoa hc cng ngh mt cch c h thng, hiu qu v thc t. Tip theo, em
xin cm n ch Nguyn Minh Quyn, hc vin cao hc, cn b nghin cu ca B mn
Vt liu bn dn cu trc nan v hng dn qu trnh thc nghim.
Em xin cm n ti cc thy c gio v cc cn b ca trng i hc Cng ngh - i
hc Quc gia H Ni ging dy, ch bo tn tnh v chu o, gip em c nhng bi hc
rt b ch v tch ly nhng kin thc qu bu trong qu trnh hc tp hon thnh
kha lun, ng thi hon thin nhng kin thc khoa hc cho cng vic hc tp v
cng tc sau ny.
Tip theo, em xin gi li cm n chn thnh ti ban ch nhim, cc thy c
gio, cc cn b ca khoa Vt l k thut v Cng ngh nan, Phng th nghim cng
ngh Nan nhit tnh hng dn, nh hng nghin cu v h tr c lc em trong qu
trnh hc tp v hon thnh kha lun.
Cui cng, em xin c cm n ti gia nh thng yu, nhng ngi bn cng lp lun
bn cnh em, quan tm v ng vin em trong cuc sng cng nh trong vic hon
thnh tt kho lun ny.
Sinh vin
L Th Vn
Tm tt ni dung
Kha lun tt nghip trnh by kt qu nghin cu v cng ngh ch to v mt s
tnh cht ca vt liu cha cc chuyn tip d cht nan.
Vt liu mng a lp v c WO3/TiO2/SnO2 vi cc chuyn tip d cht v c - v
c TiO2/SnO2, WO3/TiO2 v vt liu t hp polymer nano TiO2 cha cc chuyn
tip d cht v c - hu c MEH-PPV/nc-TiO2 c ch to.
Kho st tnh cht in sc ca h mng a lp WO3/TiO2/SnO2 bao gm ph qut
vng (CV), th mt dng thay i theo thi gian (I-t), ph truyn qua
in-situ v ph hiu sut in sc cho thy, linh kin in sc ch to t cc lp
chuyn tip d cht cho hiu sut nhum mu v p ng cao hn hn so vi linh kin
thng thng. i vi vt liu t hp cha v c-hu c vi cc chuyn tip d cht
(MEH-PPV/nc-TiO2) nhn c hiu ng dp tt hunh quang khi kch thch bng
chm tia photon c bc sng 470 nm. C ch ca hiu ng dp tt hunh quang c
gii thch do qu trnh phn li ht ti: in t chuyn ng v pha in cc trong
sut SnO2 qua chuyn tip MEH-PPV/nc-TiO2, cn l trng - v in cc kim
loi. Do vt liu t hp MEH-PPV/nc-TiO2 c th ng dng lm cht quang dn hay
vt liu cho pin mt tri hu c (OSC).LI CAM OAN
Ti xin cam oan y l cng trnh nghin cu ca ti. Kha lun khng c s sao
chp ti liu, cng trnh nghin cu ca ngi khc m khng ch r trong mc ti
liu tham kho. Nhng kt qu v cc s liu thc nghim trong kha lun cha c
ai cng b di bt k hnh thc no. Ti hon ton chu trch nhim trc nh trng v
s cam oan ny.
Sinh vin L Th Vn
MC LC
1M u
3Chng 1: Mt s vt liu quang in t v c v hu c cha cc chuyn tip khc
nhau
31.1. Cu trc vng nng lng ca mt s chuyn tip
51.2. Vt liu v linh kin in sc
61.3. Cu trc v tch cht quang ca TiO2
81.4. Polymer dn
91.4.1. Cu trc vng nng lng ca polymer dn
121.4.2. C ch truyn nng lng
131.4.3. Pin mt tri hu c (OSC)
14Chng 2: Thc nghim ch to mu
142.1. Vt liu cha chuyn tip d cht v c/v c (WO3/nc-TiO2)
152.2. Vt liu cha chuyn tip d cht hu c/v c (MEH-PPV/nc-TiO2)
162.3. Cc phng php nghin cu s dng
162.2.1. Ph quang hc
172.2.2. Ph quang hunh quang
182.2.3. Phng php o c trng in ho
22Chng 3: Kt qu v tho lun
223.1. Chuyn tip d cht v c/v c
293.2. Chuyn tip d cht v c / hu c
33Kt lun
34Ti liu tham kho
Danh mc cc t vit tt
CVCyclic votammetry ( in th qut vng )
ECDElectrochromic Device (linh kin in sc)
LUMOLowest Unoccupied Molecular Orbital
HOMOHighest Occupied Molecular Orbital
HTLHole Transport Layer (lp truyn l trng)
ITOIridium Tin Oxide
LEDLight Emitting Diode (it pht quang)
PPVPolypara-phenylene vinylene
MEH- PPVPoly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene
vinylene]
nc-TiO2Nanocrystalline titanium dioxide
OLEDOrganic Light Emitting Diode (it pht quang hu c)
PLPhotoluminescence
WEWorking electrode
SCE Saturate colomel electrode
CECounter electrode
OSCOrganic solar cell
M u
Cc linh kin vi in t, quang in t v quang t cng ngy cng c gim thiu
v kch thc v nng cao hiu sut. l nh c s pht trin rt nhanh ca cng ngh
micro v nano. Vi vic ch to cc lp chuyn tip khc nhau chng ta c th to
ra cc loi linh kin quang in t khc nhau. V d, cc chuyn tip p-n,
p-n-p, n-p-n, trong cht bn dn (Si hay Ge) to ra linh kin bn dn nh
it chnh lu, transistor. T cc cht bn dn hai hay ba thnh phn t cc vt
liu GaP, GaAs, GaInP, cc chuyn tip tng t to ra it pht quang (LED),
laser bn dn, l cc chuyn tip d th (t mt cht bn dn cng cu trc tinh th
to ra cc cht loi n hay p). Cc chuyn tip d cht c hiu l bin tip xc ca
hai hay ba loi vt liu khc nhau v cu trc tinh th v thnh phn cu to,
th d bin tip xc ca kim loi - xit - bn dn (MOS) hay bin tip xc ca
cht v c - hu c/polymer. Cc chuyn tip d cht, c bit l chuyn tip d cht
cu trc nan c nhng tnh cht mi l th, t cc chuyn tip ny c th to ra
nhiu linh kin kch thc nh, nng lng tiu th thp v hiu qu cao. Nht l
trong tnh hnh nng lng ton cu hin nay vic nghin cu ch to ra cc linh
kin tiu th t nng lng, hiu sut cao, thn thin mi trng v c bit l tn
dng c ngun nng lng di do ca mt tri l hng i c u tin hang u. ti:
Nghin cu chuyn tip d cht nano ng dng trong cc linh kin quang ha-in
t l mt dng chy ng gp vo bin ln ca khoa hc cng ngh th k XXI.Vi mc ch
nghin cu, tm kim mt s tnh cht mi ca vt liu cha cc chuyn tip d cht
cu trc nano chng ti ch to hai loi chuyn tip d cht: v c /v c
(WO3/nc-TiO2) v v c / hu c (MEH-PPV/nc-TiO2), trong nc-TiO2 l k hiu
ca cc ht xit titan c kch thc nano (trung bnh 20 nm). Nghin cu v nh
gi tnh cht ca cc chuyn tip d cht nano ny cho thy chng c kh nng ng
dng cao cho vic ch to cc linh kin vi hiu sut cao hn, p ng c cc nhu
cu thc tin. ng dng lm lp truyn ht ti trong pin mt tri hu c s tng kh
nng hp th nh sng t cho hiu sut cao hn.Mc ch nghin cu:
- To mng chuyn tip d cht cu trc nan.- Nghin cu tnh cht ca cc vt
liu cha chuyn tip d cht nan.
- Qua kho st tnh cht ca linh kin ch to t chuyn tip d cht trn a
ra kh nng ng dng trong linh kin hin th in sc (ECD) v pin mt tri hu
c (OSC).Phng php nghin cu:
- Phn tch hnh thi b mt s dng hin vi in t pht x trng (FE-SEM).-
Phn tch tnh cht hp th, truyn qua v ph pht quang thng qua ph truyn
qua v ph hunh quang.
- Phn tch tnh cht trao i ion, kh nng tim thot ca cc ion qua
chuyn tip d cht thng qua php o ph in th qut vng (CV) v ng cong I-t.
Ni dung kha lun:
B cc kho lun gm ba phn: - Phn m u.- Phn ni dung c ba chng:
+ Chng 1: Trnh by tng quan phn tch ti liu lin quan n cc chuyn
tip d th v d cht.+ Chng 2: Trnh by thc nghim ch to mu.
+ Chng 3: Trnh by cc kt qu nhn c t thc nghim v phn tch cc kt qu
trn c s cc ng cong in ho, ph quang hc v quang ph. T so snh tnh u
vit ca vt liu cha cc chuyn tip d cht so vi vt liu truyn thng.- Phn
kt lun.Chng 1: Mt s vt liu quang in t v c v hu c cha cc chuyn tip
khc nhau 1.1. Cu trc vng nng lng ca mt s chuyn tip Chuyn tip d cht
c gi l bin tip xc ca hai cht khc nhau v cu trc tinh th v thnh phn
cu to tn ti trong cht rn. i vi chuyn tip d cht ca cc cht bn dn th
hai cht thng l khc nhau v b rng vng nng lng cm v cc tnh cht khc
nhau nh: i lc ha hc, hng s in mi, khi lng hiu dng v linh ng ca cc
ht dn, v.v [1]Th d s vng nng lng ca mt s chuyn tip d cht v c c minh
ho trn hnh 1.1.
(a)
(b)
Hnh 1.1. S vng nng lng ca chuyn tip d cht N-P (a) v P-N (b)Mc
chn khng (vacuum level) l mc nng lng st b mt thay i lin tc khi i
qua bin gii, cn mc nng lng y vng dn EC v nh vng ha tr EV khng lin
tc m c cc bc nhy tng ng ECv EV khi i qua bin gii t vt liu 1 c i lc
ha hc sang vt liu c i lc ha hc.
Hiu th tip xc gia hai vt liu c xc nh t s t s vng nng lng:
(1.1)Trong v l un cong vng nng lng trn b mt vt liu 1 v 2 tng
ng.
S tn ti cc bc nhy th nng v QUOTE
c th dn n hin tng phun ht dn mt chiu trong phn cc thun ca chuyn
tip t bn dn vng cm rng sang vng cm hp. Trong chuyn tip d cht cn c
th xy ra hin tng siu phun (superinjection), l kh nng c th nhn c nng
ht dn c bn trong bn dn vng cm hp cao hn c nng ht dn c bn trong bn
dn vng cm rng. Hiu ng siu phun ny c ng dng trong LASER bn dn chuyn
tip d cht kp nh hiu ng nht ht ti (carrier confinement) lm tng hiu
sut pht x v gim dng ngng ca LASER. S dng cc cu trc d cht hn hp hoc
cc lp mng c ch to t cc cht hu c khc nhau c i lc in t khc nhau l mt
cch c th nng cao hiu sut cc linh kin quang in t hu c. Cc tip xc d
th ca cc polymer vi cc cht truyn in tch (nh cc xit kim loi, cc
polymer kt hp) c nghin cu rng ri vi mc ch lm tng hiu sut chuyn i
cng sut ca cc linh kin quang in t polymer. Bng cch to ra cc v tr
phn ly exciton theo cp bi s, cng nh cc cch truyn in tch i vi cc in
t v l trng, c hiu sut phn ly v bt gi in tch c th c tng bng cch s
dng cc tip xc d th. S dng cc tip xc d th em li nhng li ch sau: [3]
Gia tng pht sinh in tch, do c rt nhiu vt liu c di hp th khc nhau c
kt hp lm gia tng mt cc in tch.
Gia tng s phn ly in tch l do din tch bin phn cch ln hn, c bit l
cc hn hp hoc hn hp ht nan v cc lp, lm tng mt bin phn cch thch hp
cho s phn ly in tch.
Gim xc sut ti hp in t - l trng, l do l trng c truyn i qua mt vt
liu v in t qua vt liu khc, gp phn lm tng dng quang in khi c nh sng
thch hp chiu di.
1.2. Vt liu v linh kin in sc
Hiu ng in sc l hin tng vt liu biu hin s bin i thun nghch tnh cht
quang ca vt liu di s tc ng ca in trng phn cc tng ng p vo vt liu
[9]. Mt biu hin c bn ca hiu ng ny l s thay i mu sc ca vt liu khi c
t trong in trng.
Vt liu in sc do c trng c bn l s thay i tnh cht quang nn thng
thng vt liu c ch to di dng mng mng. c th ng dng tnh cht in sc ca vt
liu, ngi ta thng ch to mng mng in sc trn nn cc in cc dn in trong
sut to thnh h thng linh kin in sc. Khi p in trng phn cc vo vt liu
in sc, ty thuc vo loi vt liu v chiu phn cc ca in trng m ta c th
quan st thy trn vt liu c qu trnh thay i mu sc mt cch r rng.
Hnh 1.2. M hnh cu to mt linh kin in sc (ECD)Nguyn l hot ng ca
linh kin in sc:Khi p mt in trng ln cc in cc trong sut, cc ion s c
tim vo hoc thot ra khi lp in sc dn n s thay i tnh cht quang m c th
l s thay i mu sc, qua th hin tnh cht c trng ca linh kin. l cc linh
kin c kh nng bin iu ph truyn qua v ph phn x thng qua s thay i ln v
truyn qua v phn x.
Vt liu in sc c nghin cu nhiu l WO3. Tnh u vit ca WO3 d trng thi
v nh hnh hay tinh th n u th hin tnh cht in sc. Khi cha c tim ion v
in t, mng oxit vonfram c truyn qua cao trong vng kh kin. Ngc li khi
cc ion kch thc nh nh proton ( H+) hay c ion kim loi kim ( Li+,
Na+...) c tim vo mng th truyn qua ca chng gim i ng k. c bit hn,
trong kha lun ny, chng ti nghin cu tnh cht ca chuyn tip d cht in sc
trong h mng a lp WO3/TiO2/SnO2.C ch xy ra hiu ng in sc:
Qu trnh in sc xy ra trong cc vt liu in sc v c l kt qu ca s trao
i ion v in t lm thay i mc oxy ha ca cc tm kim loi. Qu trnh ny xy ra
theo phng trnh in ha:
MeOn + x.e + xM+ MxMeOn
Khng mu Nhum mu
Trong MeOn l oxit kim loi in sc
M+ l cation ( thng Na+ , Li+, )1.3. Cu trc v tch cht quang ca
TiO2Titaniumdioxide TiO2 l mt loi vt liu rt ph bin trong cuc sng
hng ngy ca chng ta. Chng c s dng nhiu trong vic pha ch to mu sn, mu
men, m phm v c trong thc phm.
TiO2 tn ti di 3 dng tinh th l: rutile, anatase v brookite. TiO2
l vt liu c t trng cao v c bn trn th trng. Hp cht ny c chit sut cao
vt tri, tnh tr tt v gn nh khng mu. Cu trc ca rutile xp cht kht hn
tinh th anatase. Tinh th titaniumdioxide- TiO2 c nhiu dng th hnh
trong c 2 dng th hnh chnh l:
Hnh 1.3. Cu trc tinh th ca TiO2 dng anatase
Hnh 1.4. Cu trc tinh th ca TiO2 dng rutileTuy nhin trong tinh th
anatase cc a din phi tr 8 mt b bin dng mnh hn so vi rutile, khong
cch Ti-Ti ngn hn v khong cch Ti-O di hn. iu ny nh hng n cu trc in t
ca hai dng tinh th, ko theo s khc nhau v cc tnh cht vt l v ha
hc.
Mng titanium dioxide (TiO2), c ng dng rng ri trong nhiu lnh vc k
thut nh knh lc, pin mt tri, sensor quang, knh chng phn x, v.v...
Trong thi gian gn y TiO2 c ph ln b mt cc loi vt liu dit khun, lc
khng kh, chng ru cng nh gip b mt vt liu c kh nng t lm sch, chng sng
bm, nc ng.
Hnh 1.5. Cu trc vng TiO2
Hnh 1.6. Gin nng lng ca anatase v rutile [10]Anatase c nng lng
vng cm l 3,2 eV, tng ng vi mt lng t nh sng c bc sng 388nm. Rutile c
nng lng vng cm l 3,0 eV tng ng vi mt lng t nh sng c bc sng 413
nm.1.4. Polymer dn Phat hin v tinh cht phat quang cua polymer
p-phenylenevinylene (PPV) do Bradley v cc cng s vo nm 1990 a m ra
hng nghin cu c bn va ng dung vt liu phat quang hu c [4]. o la cac
polymer dn in hay cn gi l bn dn hu c. Nhng polymer quan trong ca
nhom nay la poly (N-vinylcarbazole) vit tt la PVK,
p-phenylenevinylene vit tt la PPV,
poly(2-methoxy,5-(2'-ethyl-hexosy)-1,4-phenylene-vinylene vit tt l
MEH-PPV, v.v... Phn ln nhng hin tng quang in c bit n i vi cht ban
dn v c u tim thy nhng polymer dn nay. Cac thit bi quang in hiu sut
cao c ch tao t cac polymer kt hp chu yu bao gm: it, it phat quang,
photoit, tranzitor hiu ng trng, trit, ng in hoa phat quang, bung vi
cng hng laser... Cac linh kin ch tao t cac polymer dn co cu trc nh
gn, mng (chiu dy vi trm nanmt), trng lng nh, din tch pht quang rng,
ph pht quang phong ph, c th at hiu sut bng hoc cao hn so vi cac
linh kin tng ng ch tao bng cac cht v c Hn na, cng ngh ch to chng n
gian hn nhiu, iu ny rt c ngha, cho php sn xut i tr thnh sn phm thng
mi v h gi thnh sn phm.
Cc nghin cu cho thy cc tnh cht quang, in ca polymer v linh kin s
a dng v phong ph hn nu chng c kt hp vi cc ht nan v c (thng s dng
TiO2) hoc cc chm lng t to thnh t hp hu c-v c cu trc nan nh
MEH-PPV/TiO2, MEH-PPV/CdS (lm lp pht quang), PVK/TiO2,
PEDOT:PSS/TiO2, PVK/CdS (lm lp truyn l trng)...
1.4.1. Cu trc vng nng lng ca polymer dnPolymer dn l hp cht hu c,
m phn t ca n c xy dng nn t nhng khi c bn l cc vng benzene, bao gm
cc chui ccbon di m trong cc lin kt n C-C v i C=C lun phin k tip
nhau. Polymer dn l nhng ng ng ca benzene, lin kt gia cc phn t c thc
hin bng lc Van der Waals v s chng cho ca cc hm sng ca in t. Do c cu
trc ca vng benzene nn trong phn t polymer kt hp c rt nhiu lin kt i
(hay cn gi l lin kt ) km bn vng dn n trng thi bt nh x ca in t bao
ph ton b chui polymer. Cc tnh cht in trong c kh nng dn in ca
polymer kt hp u c ngun gc t nhng in t .
Trong polymer dn cng tn ti rng vng cm nh trong bn dn v c. S chng
chp qu o ca in t trong lin kt dn n s tch thnh hai mc nng lng: mc
nng lng lin kt v mc nng lng phn lin kt *. Mc nng lng c gi l mc HOMO
(vit tt ca ting Anh highest occupied molecular orbital : qu o phn t
in y cao nht), mc nng lng * c gi l mc LUMO (vit tt ca ting Anh l
lowest unoccupied molecular orbital : qu o phn t khng in y thp nht)
(hnh 1.7). S tch thnh hai mc nng lng ny dn n s hnh thnh hai vng nng
lng tng ng LUMO v HOMO, chng c tnh cht ging nh vng dn v vng ho tr
ca bn dn v c. Khe nng lng c to thnh gia hai mc HOMO v LUMO c gi l
vng cm ca polymer dn. Cc polymer dn khc nhau c rng vng cm khc nhau.
Khi nhn nhng kch thch ph hp t photon, in trng, cc in t c th nhy t
mc HOMO ln mc LUMO to ra cp in t-l trng (exciton), trong khong thi
gian ngn (c pic giy), cp in t-l trng (exciton) ny ti hp v pht quang
(hnh 1.8) [ 6].
Hnh 1.7. Gin mc nng lng LUMO, HOMO v rng vng cm ca polymer
dn
Hnh 1.8. Mi quan h gia HOMO, LUMO, i lc in t v th ion ho
Gi tr rng vng cm ca cc polymer dn thng c gi tr vi eV. Nng lng a
mt in t t mc HOMO ln mc chn khng gi l nng lng in ho (th tng tc ion
ho Ip) ca phn t. Nng lng a mt in t t mc chn khng v mc LUMO gi l di
lc in t (Ic) hay i lc in t ca phn t. Qu trnh chuyn in t ra khi mc
LUMO (qu trnh ion ho) lm cho phn t tch in dng, tng ng vi qu trnh dn
l trng. Ngc li, qu trnh thm in t vo mc LUMO lm cho phn t tch in m,
tng ng vi qu trnh dn in t.
Cu trc ha hc v cu trc vng nng lng ca MEH-PPV c th hin trn hnh
1.9. MEH-PPV c rng vng cm MEH-PPV c 2,8 eV thng c s dng lm lp pht
quang nh sng mu (em 590nm trong OLED (hnh 1.10) nh trong linh kin
cu trc ITO/MEH-PPV/Al.
(a)(b)
Hnh 1.9. Cu trc ha hc ca MEH-PPV-(a) v cu trc vng nng lng thch
hp vi vai tr lp pht quang (nh c minh ha trong linh kin
ITO/MEH-PPV/Al)-(b) Do MEH-PPV c mc HOMO gn mc Fecmi ca ITO, mc
LUMO gn mc Fecmi ca Al nn ro th ti cc tip xc ITO/MEH-PPV v
Al/MEH-PPV thun li cho vic bm l trng v in t vo MEH-PPV (hnh 1.9
b).
Hnh 1.10. Ph hp th v hunh quang ca MEH-PPV [14]MEH-PPV c dn p ng
c cc yu cu c bn i vi vt liu pht quang: kh nng truyn in t tt, chn c
l trng, di ph pht quang nm trong vng nh sng nhn thy v rt nhy vi mt
ngi.
c bit d ha tan trong cc dung mi hu c, d tri mng, khng yu cu nhit
cao, c kh nng tng c sn xut vi din tch ln. 1.4.2. C ch truyn nng lng
Khi cc phn t cht cho b kch thch t trng thi c bn bng s hp th nh sng
hoc nng lng in ln trng thi c mc nng lng cao hn. C th nhn bit c nng
lng ca n bng cc qu trnh hi phc pht x hoc hi phc khng pht x v trng
thi nn hoc vi s c mt thch hp ca cc phn t nhn m cc qa trnh truyn nng
lng c th xy ra.
Truyn nng lng kch thch t cht cho sang cht nhn c m t bng ba qa
trnh, l: (i) truyn nng lng Frster ca cc exciton singlet trong cht
nn sang cht nhn trong trng hp phm vi bn knh truyn ln, (ii) truyn
nng lng Dexter ca cc exciton singlet v triplet c to ra trong nn
sang cht c pha trn vo trong nn v (iii) s to thnh trc tip cc exciton
singlet v triplet trong cht nhn (trong trng hp cht nn ng vai tr l
mi trng truyn in tch.
Hnh 1.11. Cc qu trnh thuc in t ca cc phn t cht cho - cht nhn,
trong cc phn t cht nhn c th pht x bng c trng thi singlet v triplet
[13]
Trong qa trnh truyn in tch, rng vng cm ca cht nhn s an xen vo
trong vng cm ca cht cho to iu kin cho s truyn cc in t v l trng t
cht cho sang cht nhn, chng s ti hp. i vi mt h cht cho - cht nhn hiu
qu, c rt nhiu nhn t lin quan, bao gm: s tng thch ng b pha ca cht
cho - cht nhn, s kt t ca cc phn t, mc nng lng cht cho - cht nhn, s
lin kt orbital.
Hnh 1.12. Gin cu to ca pin mt tri kiu PON cu trc
ITO/TiO2/MEH-PPV/Au [3]
1.4.3. Pin mt tri hu c (OSC)
Pin mt tri hu c l linh kin quang in t hu c c cu to ging nh OLED,
nhng c nguyn l hot ng ngc li. Di tc dng ca nh sng, in t v l trng c
hnh thnh trong nn polymer (lp hot ng-active layer), hnh thnh cc
exciton vi xc sut nht nh. Trong cc pin mt tri s dng mng polymer
thun nht, cc exciton b phn ly ti b mt tip xc in cc/polymer v truyn
in tch vo cc in cc, to ra dng in mch ngoi. Vi vic s dng vt liu bn
dn hu c, M v Nht ch to c OSC vi hiu sut 10-11%. Vt liu nano TiO2 c
s dng lm in cc trong cc loi pin mt tri cm ng cht mu
(DSSC-Dye-sensitized Sollar Cells).
Chng 2: Thc nghim ch to mu
Trong chng ny ti trnh by cng ngh ch to hai loi mu bng hai phng
php khc nhau: Vt liu chuyn tip v c v c WO3/nc-TiO2 c ch to bng phng
php lng ng in ho (Electrochemical deposition); Vt liu chuyn tip v c
hu c MEH-PPV/nc-TiO2 c ch to bng phng php quay ph li tm
(spin-coating).
2.1. Vt liu cha chuyn tip d cht v c/v c (WO3/nc-TiO2) Tin hnh ch
to mng WO3/nc-TiO2 bng cch lng ng in ha mng WO3 trn thy tinh quang
hc c ph sn mng nano TiO2 xp. Thit b s dng l my Autolab PGS12
POTENTIOGALVANOSTAT. Mu c lm sch bng rung siu m vi aceton, cn, nc
ct, sy kh v em i lng ng in ha. Trong qu trnh lng ng mng WO3 in ha,
cht in ly c chng ti s dng y l dung dich axit peroxotungstic, cng c
th dng mui Na2WO4.2H2O trong dung dch axit H2SO4. Vic iu ch dung
dch axit peroxotungstic c tin hnh bng cch ha tan 4.6g bt kim loi
volfram tinh khit trong 25ml dung mi peoxithydro (H2O2) 30% thu c
dung dch peroxotungstic (H2W2O11) Sau khi lng kim loi W ha tan hon
ton, b sung mt lng nc ct vo c 500ml dung dch axit peroxotungstic
50mM. nhit cao dung dch ny khng bn d b phn hy thnh dng trioxit
polytungtate, v vy cn c bo qun mi trng kh, mt. Vic to mng c thc hin
bng phng php th khng i Potentiostatic. Trong bnh in ha ba in cc, in
cc lm vic (WE) l thy tinh c ph lp in cc trong sut lm sch, in cc i
(CE) l in cc platin (Pt) v in cc so snh l in cc calomel bo ho
(SCE). in p ti u trn in cc lm vic c thit lp l -500mV so vi in cc so
snh (-500mV/CSE).
Hinh 2.3. Qu trnh o v lng ng WO3. Trn hnh l h in ha trong chn
platin kt ni vi h o Autolab PGS12 POTENTIOGALVANOSTAT, php o c tuyn
dng th c thc hin bng phn mm trn my tnh2.2. Vt liu cha chuyn tip d
cht hu c/v c (MEH-PPV/nc-TiO2)Bng 2.1. Cc bc ch to mng
MEH-PPV/nc-TiO2
Xc nh in tr ca in cc ITO trn thy tinh bng ng h vn nng.
S dng ethanol rung siu m nhm ra sch nhng tp bn b mt mu ri sy
kh.
Quay ph ly tm to mng mng nano MEH-PPV nn mu . Tc quay ph : 1500
vng/pht, trong 1pht, nhit phng.
Qu trnh nhit c thc hin ti 800C trong chn khng 102 Torr, thi gian
l 5 gi. B mt mu chuyn sang mu cam nht khi cc dung mi hu c v cht hot
ng b mt kh, v b xi ha hon ton to thnh lp MH-PPV mu cam nht.
Mng d cht hu c /v c (MEH-PPV/nc-TiO2) c ch to ti phng th nghim
ca Khoa vt l k thut, i Hc Cng Ngh bng phng php quay ph ly tm. y l
phng php n gin v rt ph hp khi ch to mng polymer dn in. Phng php ny
c th to ra mng vi chiu dy ng nht do s cn bng gia lc li tm (hng ra
ngoi) v lc nht (hng vo trong), khng lm thay i cu trc, chiu di chui
polymer, khng i hi chn khng cao nh cc phng php lng ng pha hi vt l.
Quy trnh ch to n gin l mt trong nhng u im ni tri c la chn ch to cc
linh kin quang in t hu c, c bit l cc OLED v pin mt tri, v n cho php
gim gi thnh sn phm v c th a vo sn xut i tr, bin thnh cc sn phm thng
mi.
thc hin qu trnh quay ph, trc tin tin hnh to dung dch MEH-PPV bng
cch ha tan bt MEH-PPV vo dung mi chlorform hoc Toluen. T l 2mg
MEH-PPV/1ml dung dch chloroform. Sau rung siu m nhiu ln (trnh nh
sng) ho tan bt hu c hon ton. Dung dch MEH-PPV c em quay ph ly tm to
mng trn thy tinh quang hc ph sn mng nano TiO2 xp (bng 2.1).Trong qu
trnh quay ph ly tm, vt liu hu c di dng cht lng c ph trn b mt . Tm c
quay vi tc cao cht lng tri u b mt mu. dy lp ph t c t vi trm nm n 10
m. Mu ch to c sau em trong l chn khng ti nhit 800C trong chn khng c
102 Torr vi thi gian l 5 gi (s dng l nhit chn khng Nabertherm
P320).Sau khi ch tao, cc mu c kho st cc tnh cht thng qua cc php o
quang, quang ph, in ho.2.3. Cc phng php nghin cu s dng2.2.1. Ph
quang hc Ph hp th biu th mi quan h gia cng hay h s hp th nh sng ca
vt liu vi bc sng nh sng chiu vo vt liu. Php o ph hp th quang hc cho
ta rt nhiu thng tin v vt liu nh: rng vng cm quang, d on bc sng hunh
quang ca vt liu nu vt liu pht quang, hiu ng kch thc lng t, c tnh
kch thc ca cc chm lng t, v cc dch chuyn quang hc... Trong lun n,
php o ph hp th c la chn xc nh rng vng cm ca mng polymer thun nht,
mng polymer t hp cu trc nan (da vo cng thc trong (ab l bc sng ng vi
nh ph hp th), nghin cu s s nh hng ca cc ht nan TiO2 ln hp th ca mng
t hp. Ngoi ra php o cn cho bit v chiu di lin kt (conjugation
length) ca chui polymer trong mng t hp cu trc nano so vi chiu di
lin kt ca mng polymer thun nht, s inh x ca cc in t linh ng ( dc
chui polymer da vo kt qa dch nh ph hp th v pha sng di (red-shift)
hay sng ngn (blue-shift). S dch nh ph v pha sng di chng t chiu di
lin kt ca chui polymer tng, do s xen ph v nh x ca cc in t ( dc chui
polymer tng dn n gim rng vng cm ca vt liu t hp so vi vt liu thun
khit. Ngc li, s dch nh ph v pha sng ngn chng t chiu di lin kt ca
chui polymer gim, do s xen ph ca cc in t ( dc chui polymer gim dn n
s m rng vng cm ca vt liu t hp so vi vt liu thun khit. Trong kha
lun, cc php o ph hp th ca cc mu c thc hin trn h o UV-VIS-NIR Jasco
V570 ca trng i hc Cng ngh - i hc Quc gia H Ni (Hnh 2.5)
Hnh 2.5. H o ph hp th UV-VIS Jasco V-5702.2.2. Ph quang hunh
quang Ph hunh quang biu din mi quan h gia cng hunh quang v bc sng
pht quang khi vt liu nhn nh sng kch thch no . Ph hunh quang cho bit
bc sng pht quang, cc dch chuyn quang hc ca in t ca cc tm pht quang,
cc qu trnh truyn nng lng gia cc tm pht quang( Vi mc ch nghin cu ca
ti, chng ti s dng ph hunh quang nghin cu hiu ng dp tt quang hunh
quang, bng cch so snh cng pht quang ca mu t hp so vi mu thun khit.
Trn c s kt hp vi cc ti liu tham kho khc, cho php kt lun v s phn ly
v truyn in tch ti bin tip xc polymer/nan. Kt qa o ph hunh quang c
kt hp vi kt qa o ph hp th a ra kt lun chnh xc hn v chiu di lin kt
ca chui polymer trong mu t hp so vi mu thun khit. Nguyn l ca php o
ph hunh quang ca polymer dn: polymer dn c tri mng trn cc thu tinh
thng hoc thu tinh ITO, c kch thch bi laze hoc n ph rng Xenon. Di tc
dng ca nh sng kch thch, cc in t mc HOMO ca polymer dn nhn nng lng
kch thch s chuyn ln mc LUMO ca polymer, to ra cp in t l
trng-exciton. Sau mt khong thi gian rt ngn, c vi trm pic giy, cp in
t - l trng ti hp v bc x, to ra hunh quang. Tn hiu pht x hunh quang
c ghi nhn detector ca my o hunh quang v c lu gi di dng cc file d
liu. Phn mm Origin c dung x l s liu di dng ph hunh quang. H thng o
hunh quang c s dng trong ti l my o hunh quang phn gii cao dng laze
He-Cd bc sng 337.1 nm ca Vin khoa hc vt liu (hnh 2.6).
Hnh 2.6. H o hunh quang phn gii cao dng laser He-Ne2.2.3. Phng
php o c trng in ho Theo phng php ny, in th c bin thin tuyn tnh theo
thi gian, in th c t vo hai u in cc (catt v ant) ca linh kin v c qut
i qut li trong phm vi 0 10V vi tc qut khng i. Khi dng qua in cc tng
ng c xc nh. Cc php o c tin hnh trn h Autolab - PGS - 30 ca khoa Vt
l k thut & cng ngh nan - trng H Cng ngh - H Quc gia H Ni (hnh
2.7).
Hnh 2.7. H o in ho Auto.Lab-Potentiostat PGS-12T ngun in xoay
chiu 220V, nh bin p v b nn dng, c ngun in mt chiu - c iu khin. Thay
i in p mt chiu t ln mu, tng ng c dng mt chiu bin i theo. Cc gi tr
ny c ghi li nh h ng h Keithley 2000 v my tnh COMPAQ. ng c trng I-V
cn c kho st theo nhit mi trng xung quanh mu c hai vng nhit trn v di
nhit cho php nh thit b iu nhit ELN-U15c v EF.
Ph in th qut vng o (CV) c th o trn mu ba hc hai in cc. Trong
phng php ba in cc, c ba in cc (TiO2/ ITO, SCE v Pt) c nhng trong
dung dch cht in phn LiClO4+ PC hoc WO3 . Nh b phn cc in p PGS-30 v
h iu hnh CPU, in cc lm vic TiO2/ITO v in cc i Pt to thnh mt cp in
cc c in tch tri du, bin i tun hon so vi in cc chun SCE (Hnh
2.9).
Khi in cc lm vic TiO2/ITO c in th m/SCE, th cht in ly Li+ hoc
W3+ (cation c kch thc nh) chuyn ng v pha catt v chui vo trong mng
TiO2, qu trnh xy ra ngc li khi in cc ny c in th dng/SCE. in th qut
vng trn in cc lm vic to ra cho TiO2 tch - thot ion c kch thc nh nh
Li+, H+, Na+. Kh nng tch-thot ny c kho st trn th mt dng ph thuc vo
in th qut vng t vo mng TiO2, quan st s thay i mu ca n. Cc kt qu o,
c ghi v lu li nh my tnh PC.
Hnh 2.9. S o in th qut vng (Cyclic voltametry) Da vo c tuyn I-V
ta nh gi c cc tnh cht in ca mu nh: s ph thuc ca cng , dng v hiu in
th, in tr ni, dng ngc, n nh ca linh kin.2.2.5. Phng php o knh hin
vi in t qut FE-SEM
Hin vi in t qut pht x trng (FE-SEM) l phng php SEM c phn gii cao
hn mt bc so vi SEM thng thng. V vy s dng FE-SEM c th chp cu trc ht
nan tinh th vi nt rt cao. SEM hot ng theo nguyn l sau: in t th cp
pht x nh cc in t ca sng in t c nng lng cao bn ph vo b mt ca mu kho
st. S lng in t th cp pht x cng nhiu khi b mt mu nh ln cng cao v ngc
li khi b mt b lm xung, tng ng vi nhng im sng - ti c hin trn nh nh b
chuyn i tn hiu t in t pht x sang nh sng nhn thy.
Trn hnh 2.11 knh hin vi in t qut chp vi nh b mt. in t c gia tc
trong in trng to bi cao p iu khin t (0 ( 30) KV hoc ln ti 60 KV tu
thuc vo thit b v mu kho st c hi t vo ca AS nh thu knh L1. Chm in t
i qua cun qut (SC) hi t nh knh vt L2 vo mu S pht x ra in t th cp i
vo ng gp C. Qu trnh c thc hin trong bung chn khng p sut c 10-4Torr.
Nh my khuch i A thng tin c truyn vo thit b ghi nh PR ca ng tia catt
CRT. Nng sut phn gii ca knh hin vi in t qut b gii hn bi kch thc ca
chm tia in t chiu vo mu. phn gii ca SEM t vo c 6 ( 3 nm trong trng
hp c pht x trng (FE). Cc mu nghin cu c chp trn h FE-SEM ca Phng th
nghim trng im-Vin Khoa hc Vt liu (Vin Khoa hc Cng ngh Vit Nam).
Hnh 2.10. My FE-SEM Hitichi - S4800 Chng 3: Kt qu v tho lunNhiu
linh kin bn dn, linh kin in sc hin nay nh OLED, pin mt tri, u l loi
a lp, vi t hp nhiu chuyn tip d cht. Nhng chuyn tip d cht nano v c/v
c, hu c/v c gip cho linh kin a lp c hiu sut co hn linh kin n lp m
vn m bo vi kch thc. V d nh lp chuyn tip d cht WO3/TiO2 , TiO2/SnO2
lm gim hng ro Schottky, thc y qu trnh truyn ht ti (in t) t in cc
trong sut sang lp in sc, ng thi thc hin c hiu ng ECD ca c TiO2 v
WO3 iu ny c tc dng nng cao hiu sut in sc ca linh kin in sc a lp so
vi n lp; chuyn tip d cht MEH-PPV/nc-TiO2 gip tng di nh sng hp th ca
pin mt tri. 3.1. Chuyn tip d cht v c/v c
Chuyn tip d cht v c/v c (WO3/TiO2) c ch to bng cch ph in ho WO3
ln trn in cc TiO2/SnO2 xp nano (in cc ny c ch to bng phng php ph
tri doctor blade [8]. Hnh 3.1 cho thy cc ht nano tinh th TiO2 sp xp
chng ln nhau, to ra nhiu knh dn nano.
Hnh 3.1. nh FE-SEM chp trn b mt mu TiO2/SnO2
S dng phng php in th khng i, mng WO3 c ph trn in cc lm vic (WE)
nc-TiO2/SnO2. Ch sau 50 giy mt dng t gi tr bo ho (Hnh 3.2). Sau mng
vn tip tc dy ln, nhng tc ph gim dn cho n khi t gi tr 500 nm th khng
dy thm na. Trong 10 giy u tin, tc ph t gi tr cao, khong 10
nm/s.
Hnh 3.2. Mt dng ph thuc thi gian trong khi ph in ho vi in th
khng i - 2,5 V/SCEBng vic khng ch thi gian ph c th nhn chiu dy ca
mng t 50 nm n 500 nm. Trong thc nghim chng ti ph mng WO3 dy khong
300 nm, thi gian 120s. Nh vy tc ph trung bnh l 2,5 nm/s. nghin cu
tnh cht truyn ht ti qua bin tip xc (chuyn tip d cht) t cht ny sang
cht khc chng ti s dng cc php o in ho nh ng cong tim thot ion I-t v
ph qut vng CV (cyclic votammetry).
Hnh 3.3 trnh by th m t qu trnh tim / thot ion Li+ vo / ra in cc
a lp WO3/TiO2/SnO2.
Hnh 3.3. th tim thot ion Li+ trong qu trnh ECD: 5 chu k nhum v
ty mu ng vi in th - 2,5 V/SCE v + 0,5 V/SCE;Thi gian nhum 5s v thi
gian ti 20sT hnh 3.3 c th tnh c in lng (Q) tim vo v thot ra ca qu
trnh in sc. th trn cng cho thy qu trnh nhum ECD (5 giy) xy ra nhanh
hn qu trnh ty (20 giy). y l s liu trch ra t kho st qu trnh ECD sau
hn 100 chu k. iu ny chng t linh kin ECD khng b gi ho nhanh. Vic tim
vo v thot ra ca Li+ xy ra mt cch thun nghch - mt tnh cht quan trng
ca linh kin ECD trong ng dng thc tin.Trn hnh 3.4 l ph CV ca in cc
lm vic WE cu trc a lp WO3/TiO2/SnO2 qut trong cht in li 1M LiClO4
trong propylene carbonate (LiClO4+PC). Theo chiu qut dng (PSD) c 2
nh ca mt dng ti in th -1.0 V/SCE v ti 0.32 V/SCE. Theo chiu qut in
th m (NSD) cng c 2 nh. Ph CV chng t tnh thun nghch ca hiu ng in sc
trong qu trnh ion Li+ tim vo v thot ra khi in cc WO3/TiO2/SnO2. Phn
ng trn ant v catt theo chiu tng ng i vi mng n lp TiO2 [5] l:
TiO2 + x (Li+ + e-) ( LixTiO2
(3.1)
Hnh 3.4. Ph CV ca in cc WO3/TiO2/SnO2 qut trong LiClO4+PC (tc
qut ( = 100 mV/s)
Vi mng TiO2 ch to bng phng php sol-gel, thi gian trng thi nhum
mu t gi tr bo ha mt n 45 pht [7]. Trong trng hp mng a lp
WO3/TiO2/SnO2 hin tng nhum mu in sc xy ra nhanh hn rt nhiu. Trng
thi bo ha nhum mu t c ch sau 15 giy.
Hn na ph CV ca h mng WO3/TiO2/SnO2 qut trong dung dch LiClO4+PC
th hin khng nh mt ph tng thng thng t hai ph CV ca tng chuyn tip
ring r WO3/SnO2 v TiO2/SnO2 m l ph CV ca mt t hp. iu ny l do trong
qu trnh lng ng nhiu ion W3+ xm nhp vo trong mng TiO2, thay th Ti to
ra cu trc pha tp TiO2: W hay Ti(1-y)WyO2. Ngay trong khi lng ng hin
tng in sc trn mng TiO2 cng c quan st thy rt r. Hin tng nhum mu in
sc ny c th gii thch thng qua phng trnh phn ng trn hai in cc l:
TiO2 (trong sut) + xW3+ +xe- WxTiO2 (xanh)
(3.2)
trong TiO2 trong sut cn WxTiO2 hp th mnh nh sng kh kin, li mu
xanh xm.
Do hiu ng in sc (ECD) trn h mng a lp WO3/TiO2/SnO2 qut trong cht
in li cha ion Li+ (LiClO4+PC) c m t bi cc phng trnh:
TiO2 (trong sut) + xLi+ +xe- Lix TiO2 (xanh)
(3.3)
WO3 (trong sut) + xLi+ +xe- Lix WO3 (xanh)
(3.4)
v
Ti(1-y)WyO2 (trong sut) + xLi+ +xe- LixTi(1-y)WyO2 (xanh)
(3.5)trong y l hm lng nguyn t vonfram (nng nguyn t W) thay th Ti
trong mng TiO2.
Hiu ng ECD trn tng lp chuyn tip ring r WO3/SnO2 v TiO2/SnO2 c
nghin cu, trong linh kin in sc c s WO3/SnO2 cho n nay c a vo ng dng
trong cng nghip xe hi v ca s thng minh. Linh kin in sc a lp
WO3/TiO2/SnO2 c ch to c cu trc nh sau:
SnO2 LiClO4+PC WO3/TiO2/SnO2Ph truyn qua tc th (in-situ ) ca
linh kin ny c kho st bng cch t linh kin vo b g mu ca ph k
UV-VIS-NIR (V-570), hai in cc trong sut (SnO2) c ni vi b ngun dng
mt chiu c iu khin in th v chuyn chiu phn cc ca in trng. Kt qu ph
truyn qua in-situ c trnh by trn hnh 3.5
Hnh 3.5. Ph truyn qua in-situ ca linh kin SnO2 LiClO4+PC
WO3/TiO2/SnO2 thc hin trong LiClO4 +PC ti -2.5 V theo thi gian. ng
ph th nht (ng 1) l ph truyn qua khi khng c in th trn in cc WE. Cc
ng 2, 3, 4 v 5 ng vi thi gian nhum l 5, 10, 15 v 20sec, ng s 6 l ph
sau khi i chiu phn cc (phai mu).Trong nghin cu v vt liu in sc, qu
trnh nhum v ty mu c c trng bi i lng vt l, gi l mt quang (OD). So
snh s thay i v mt quang ((OD) ca mng in sc gia hai trng thi trong
sut (trng thi phai mu) v hp th hoc phn x (nhum mu) c th nh gi hiu
sut in sc. Nh bit:
(OD = ODc - ODb = ln(Ib(()/Ic(())
(3.6)
Trong ODc v ODb l mt quang tng ng ca trng thi nhum v phai mu;
Ib(()/Ic(() l t s gia truyn qua ca mng khi trng thi phai v nhum mu.
T hiu sut nhum mu (() ca vt liu hoc linh kin c xc nh t t s ca mt
quang trn in tch (Q) c tim vo, nh sau:
( = (OD/Q
(3.7)
th (-( ca qu trnh in sc c trnh by trn hnh 3.6 Ti ( = 550 nm,
chng ta c Q = 0.61 mC(cm-2, Tb = 78% v Tc = 10%, nn tnh c ( = 33.7
cm2(C-1. T hnh 3.6 nhn thy ti vng bc sng cng ln hiu sut ECD cng
cao. Trong vng kh kin, cc gi tr ( nhn c hon ton tng ng vi gi tr ca
hiu sut ECD trn mng WO3 [12] v ln hn hn i vi mng TiO2 ch to bng
phng php sol-gel nhng ko [7] v mng xit Ti-La lng ng bng phn x
[11].
Hnh 3.6. th biu din ph thuc ca hiu sut ECD vo bc sng i vi linh
kin a lp SnO2 LiClO4+PC WO3/TiO2/SnO2 di in th (2.5V gii thch tnh
cht in sc ca mng a lp c cha cc chuyn tip d cht chng ti xem xt cu
trc vng nng lng ca h mng ny.
Hnh 1.1 a) (phn tng quan) biu din s nng lng vng cm trn chuyn tip
n-p v p-n ca hai cht bn dn v c cng mt cu trc tinh th (th d Si-n v
Si-p) trc v hnh 1.1 b) l chuyn tip d cht ca cht bn dn loi p vng cm
rng tip xc vi cht bn dn loi n vng cm hp hn. Tuy nhin, trong trng hp
hai cht khc cu trc tinh th nhng cng loi n th s hnh thnh bin tip xc
dn n cu trc vng nng lng c hnh dng khc nh hnh 3.7.
Hnh 3.7. Chuyn tip d cht n-N trc v sau khi tip xcChuyn tip d cht
WO3/TiO2/SnO2 to ra t cng ngh ch to a lp bng cch ph doctor blade
TiO2 trn dn in trong sut (SnO2) v ph in ho WO3 trn TiO2/SnO2. Trong
trng hp ny c hai lp bin tip xc to ra hai chuyn tip d cht cng loi
n-n l TiO2/SnO2 v WO3/TiO2. S cu trc vng nng lng ca chuyn tip a lp
WO3/TiO2/SnO2 c minh ho trn hnh 3.8.
Hnh 3.8. S nng lng trn bin tip xc a lp WO3/TiO2/SnO2Vic ghp thm
lp TiO2 gia in cc trong sut SnO2 v lp in sc WO3 c hai chc nng chnh.
Th nht l gim hng ro Schottky gia hai lp, thc y qu trnh truyn ht ti
(in t) t in cc trong sut sang lp in sc; th hai l ng thi thc hin c
hiu ng ECD ca c TiO2 v WO3. C hai u im ny u c tc dng nng cao hiu
sut in sc ca linh kin a lp so vi linh kin n lp.
3.2. Chuyn tip d cht v c / hu c
Chuyn tip d cht v c/hu c c ch to bng cch tm ph trong chn khng lp
mng polymer kt hp MEH-PPV ln trn in cc xp TiO2/SnO2. Hnh 3.8 l nh
FE-SEM chp b mt mu sau khi tm ph vi chiu dy khc nhau.
Hnh 3.9. nh FE-SEM chp trn b mt mng ph MEH-PPV/nc-TiO2 vi chiu
dy lp MEH-PPV ~ 50 nm (a), 100 nm (b) v 200 nm (c)
i vi lp polymer mng c th quan st thy MEH-PPV thm thu vo cc l hng
nano v bao quanh cc ht nano TiO2 (Hnh 3.8 a). i vi cc mu c lp
MEH-PPV dy trn 100 nm, b mt ca mu mn, cac ht nano TiO2 hu nh b che
ph hon ton. Ging nh chuyn tip d cht WO3/TiO2 nu trn, cc mu c lp
polymer dy cha chuyn tip MEHPPV/TiO2 mang tnh chuyn tip mt (Hnh 3.8
b v c). Trong trng hp lp polymer mng, mng cha cc chuyn tip khi. Vt
liu ny c tnh cht ca mt t hp nano (nanocomposite), ging nh cc ht
nano xit c trn vo trong cht polymer. V th c th gi chng l vt liu t
hp nan. Nghin cu chi tit cc tnh cht ca t hp nano ng dng cho OLED c
trnh by trong [2].Trong cng trnh ny tnh cht quang ca vt liu cha
chuyn tip MEHPPV/TiO2 c nghin cu nhm so snh s khc bit ca vt liu t
hp vi vt liu polymer thun khit v kh nng ng dng ca chng trong pin mt
tri hu c (OSC).Ph hp th ca cc mu c kho st trn my quang ph
UV-VIS-NIR (V-570), kt qu o ph hp th ca mng polymer thun khit c
trnh by trn hnh 3.9.
Hnh 3.10. Ph hp th ca mng polymer thun khit MEH-PPV (A) v cc mng
t hp c chiu dy khc nhau: B: 50 nm, C: 100 nm v D: 200 nm
Ph hp th ca mng MEH-PPV tinh khit tri rng t bc sng 400 nm n 600
nm, c nh hp th ti bc sng 498 nm, tng ng vi dch chuyn (LUMO ( HOMO )
ca in t.
T ph hp th c th tnh c rng vng cm quang ca mng t hp cha cc chuyn
tip d cht ( ). Kt qu nhn c Eg = 2.05 eV. Gi tr rng vng cm ny cho
thy mng MEH-PPV c bc sng pht quang trong vng nhn thy (nh sang ). T
ph hp th c th la chn bc sng kch thch cho php o ph quang hynh quang
ca vt liu. Chng ti s dng chm bc sng 470 nm (nng lng photon trung
bnh) kch thch hunh quang ca cc mu. Cng ph hp th ca cc mu t hp gim
theo chiu tng ca lp polymer ph trn mng TiO2. Ring i vi mu mng (50
nm) nh ph hp th dch nh v pha sng ngn. iu ny c gii thch l do cc ht
xit TiO2 trn trong polymer lm ngt chui polymer, khin khe nng lng
LUMO HOMO (ging nh rng vng cm trong bn dn v c) m rng ra mt cht
[15]. Ph hp th ca cc mu c lp polymer dy ch phn nh bn cht hp th ca
polymer thun khit.Ph hunh quang ca mng MEH-PPV thun khit v cc t hp
tri rng t bc sng 570 nm n 700 nm. Ph c hai nh pht quang ti bc sng
xp x 600 (nh 1) v 630 nm (nh 2). Cng hunh quang ca nh 1 cao hn nh 2
khi c kch thch bng chm tia c bc sng 470 nm (hnh 3.9).
Hnh 3.11. Ph hunh quang ca MEH-PPV tinh khit (A) v ca cc mu t hp
c chiu dy 200 nm (B), 100 nm (C) v 50 nm (D); Bc sng kch thch 470
nmnh th nht c quy cho dch chuyn 0-0 ca cc in t khi chng mc nng lng
ng vi s lng t n = 0 ca trng thi exciton n (singlet) S1 hi phc v mc
nng lng ng vi s lng t n = 0 ca trng thi c bn S0. nh th hai c quy
cho dch chuyn 0-1 ca in t khi in t hi phc t mc nng lng ng vi s lng
t n = 0 ca trng thi kch thch n S1 v mc nng lng ng vi s lng t n = 1
ca trng thi c bn S0.
Ph quang hunh quang ca cc mu t hp v hnh dng, ging vi ph ca
polymer thun khit, nhng c hai im khc bit: th nht l cng quang hunh
quang ca mu t hp suy gim (khi c kch thch bng nh sng c bc sng 470
nm), th hai l c s dch nh ph, c hai c im ny u ph thuc vo chiu dy ca
lp ph polymer.
S suy gim cng quang hunh quang ca cc mu t hp so vi mu thun khit
(xy ra khi mu c kch thch bng nh sng c nng lng trung bnh) c gi l hiu
ng dp tt hunh quang (luminescence quenching). C ch dp tt hunh quang
ca cc vt liu polymer cha tip xc d cht c th gii thch thng qua s vng
nng lng, th hin trn hnh 3.11.
Hnh 3.12. S m t tip xc gia TiO2 vi MEH-PPV trc kch thch ( a)v
sau kch thch photon ( b) [2]Photon kch thch c nng lng xp x 2.6 eV
(bc sng kch thch 470 nm) ln hn nng lng vng cm ca MEH-PPV (2.3 eV) v
nh hn ca TiO2 (3,2 eV). Do vy cc photon ny ch kch thch c cc in t mc
HOMO nhy ln mc LUMO ca MEH-PPV, li vng HOMO cc l trng, to ra cp in
t - l trng lin kt (exciton). Trong trng hp c cc ht nan TiO2 th cc
in t kch thch truyn sang vng dn ca TiO2, l do mc nng lng ca vng dn
TiO2 nh hn mc nng lng LUMO ca polymer MEH-PPV. Do vy, s lng cp in t
- l trng trong MEH-PPV gim, dn n gim xc sut tan r exciton, nn cng
hunh quang ca cc mu t hp nh hn ca cc mu polymer thun khit. Nh vy,
trn bin tip xc (chuyn tip d cht) khi vt liu t hp c chiu di, s xy ra
hin tng tch ht ti: in t dch chuyn v pha TiO2 v in cc trong sut
SnO2, cn l trng v pha in cc kim loi (hnh 3.11). chnh l nguyn l lm
vic ca pin mt tri hu c s dng cc chuyn tip d cht cu trc nano. Pin mt
tri hu c s l ti nghin cu trong giai on tip theo.Kt lun
ch to hai loi vt liu cha chuyn tip d cht: (i) Vt liu mng a lp v
c WO3/TiO2/SnO2 vi cc chuyn tip d cht v c - v c TiO2/SnO2 v
WO3/TiO2; (ii) Vt liu t hp, polymer ph trn mng TiO2 xp nano cha cc
chuyn tip d cht v c - hu c MEH-PPV/nc-TiO2.
Nghin cu tnh cht in sc ca h mng a lp WO3/TiO2/SnO2 cho thy, nh
cc lp chuyn tip d cht, hiu sut in sc v p ng (response time) ca linh
kin ECD c ci thin ng k.
Nghin cu hnh thi hc ca vt liu t hp cha cc chuyn tip d cht v c-hu
c (MEH-PPV/nc-TiO2) cho thy, lp ph mng MEH-PPV c tc dng in y cc l
hng nano trong in cc xp TiO2, to ra t hp nano dng khi. Hiu ng dp tt
hunh quang nhn c khi chm tia photon nng lng trung bnh kch thch ln b
mt ca vt liu t hp, dn n qu trnh phn li ht ti. Nh c tnh cht ny vt
liu t hp MEH-PPV/nc-TiO2 c th ng dng lm cht quang dn v vt liu cho
pin mt tri hu c (OSC).Ti liu tham khoTing Vit
[1] Phng H-Phan Quc Ph, Gio trnh Vt liu bn dn, Nh xut bn Khoa Hc
v K Thut, 2008, tr.20-21.[2] Trn Th Chung Thy, Ch to v nghin cu tnh
cht quang v in ca vt liu t hp cu trc nan (polymer v nan tinh th
TiO2) dng cho OLED, Lun n tin s,i Hc Cng Ngh-H Quc Gia H Ni, 2010,
tr.60-68.Ting Anh [3] A.J. Breeze, Z. Schlesinger, and S. A.
Carter, P. J. Brock, Charge transport in TiO2/MEH-PPV polymer
photovoltaics, Physical Review B, Vol. 64, 125205,2001, pp.1-8.[4]
J. H. Buroughes. J. H., D. D. C. Bradley, A. R. Brown, R. N. Marks,
K. Mackay, R. H. Friend, P. L. Burns, and A. B. Holmes,
Light-Emitting-Diodes Based on Conjugated Polymers, Nature, 347
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[5] G. Campet, J. Portier, S. J. Wen, B. Morel, M. Bourrel, J.
M. Chabagno, Electrochromism and electrochromic windows, Active and
Passive Elec.Comp, vol.14, 1992, pp. 225 - 231.
[6] S.V. Chasteen, Exciton dynamics in conjugated polymer
phottovolataics: steady state and time-resolved optical
spectroscopy, Doctor of philosophy in Physics, December 2005.[7] N.
N. Dinh, N. Th. T. Oanh, P. D. Long, M. C. Bernard, A. Hugot-Le
Goff, Electrochromic properties of TiO2 anatase thin films prepared
by dipping sol-gel method, Thin Solid Films , Vol.423 , 2003, N1,
pp. 70-76 .[8] Nguyen Nang Dinh, Nguyen Minh Quyen, Do Ngoc Chung,
Marketa Zikova,Vo-Van Truong, Highly-efficient electrochromic
performance of nanostructured TiO2 films made by doctor blade
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[9] C. G. Granqvist, Solar Energy Materials and Solar
Cells,Volume 44, Issue 4, 15 December 1996, pp. 375-381.[10]
D.Hanaor, C.Sorrell, "Review of the anatase to rutile phase
transformation", Journal of Materials Science,Vol.46, 2011,
pp.120.[11] L. Kullman, A. Azens, C. Granqvist, Decreased
electrochromism in Li-intercalated Ti oxide films containing La,
Ce, and Pr, J. Appl. Phys. 81,1997, 8002-1 ( 8002-9.
[12] L. Meda, R. C. Breitkopf, T. E. Haas and R. U. Kirss,
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[13] A. Mills, S. Le Hunte, An overview of semiconductor
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[14] V. K. Sachder, R. Kumar, A. Singh, S. Kumar, and R. M.
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I HC QUC GIA H NI
TRNG I HC CNG NGH
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NGHIN CU CHUYN TIP D CHT NANO NG DNG TRONG CC LINH KIN
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KHO LUN TT NGHIP I HC H CHNH QUY
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Cn b hng dn: GS.TS. Nguyn Nng nh
H NI - 2011
I HC QUC GIA H NI
TRNG I HC CNG NGH
L Th Vn
NGHIN CU CHUYN TIP D CHT NANO NG DNG TRONG CC LINH KIN
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H NI - 2011
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