title: A strategy to increase the efficiency of the dye-sensitized TiO2 solar cells operated by photoexcitation of dye-to-TiO2 charge-transfer bands.
abstract: Dye-sensitized nanoporous TiO2 solar cells (DSSCs) can be classified into two types, namely, Type-I and Type-II. Type-I DSSCs are the DSSCs in which electrons are injected from the adsorbed dyes by photoexcitation of the dyes followed by electron injection from the excited dyes to TiO2 (pathway A). Type-II DSSCs are the DSSCs in which electrons are injected not only by pathway A but also by direct one-step electron injection from the dyes to TiO2 by photoexcitation of the dye-to-TiO2 charge-transfer (DTCT) bands (pathway B). The DSSCs employing catechol (Cat) or its derivatives as the sensitizers have been the typical examples of Type-II DSSCs. However, their solar energy-to-electricity conversion efficiencies (eta) have never exceeded 0.7%, and the external quantum efficiencies (EQE) at the absorption maximums of the DTCT bands have never exceeded 10%. We found that the attachment of electron-donating compounds such as (pyridin-4-yl)vinyl and (quinolin-4-yl)vinyl, respectively, to Cat (designated as Cat-v-P and Cat-v-Q, respectively) leads to 2- and 2.7-fold increases, respectively, in eta, driven by large increases in short circuit current (Jsc). The EQE increased from 8.5 to 30% at 400 nm upon changing from Cat to Cat-v-P, at which only the DTCT band absorbs. In the case of the Cat-v-Q-sensitized DSSC, even the eta obtained by exciting only the DTCT band was higher than 1%. Interestingly, the illumination of only the DTCT band resulted in the increase of fill factor from 62.6% to 72.3%. This paper provides for the first time an insight into the strategy to increase the eta values of Type-II DSSCs.
authors.affiliation: Center for Microcrystal Assembly, Department of Chemistry, and Program of Integrated Biotechnology, Sogang University, Seoul 121-742, Korea.
authors.forename: Eunju Lee
authors.initials: EL
authors.lastname: Tae
authors.forename: Seung Hwan
authors.initials: SH
authors.lastname: Lee
authors.forename: Jae Kwan
authors.initials: JK
authors.lastname: Lee
authors.forename: Su San
authors.initials: SS
authors.lastname: Yoo
authors.forename: Eun Ju
authors.initials: EJ
authors.lastname: Kang
authors.forename: Kyung Byung
authors.initials: KB
authors.lastname: Yoon
mesh_terms: D000327:Adsorption; D002396:Catechols / Q000737:chemistry; D004396:Coloring Agents / Q000138:chemical synthesis / Q000737:chemistry*; D011211:Electric Power Supplies; D004583:Electrons; D008956:Models, Chemical; D015394:Molecular Structure; D010777:Photochemistry; D016062:Porosity; D011725:Pyridines / Q000737:chemistry; D011804:Quinolines / Q000737:chemistry; D013237:Stereoisomerism; D013499:Surface Properties; D013696:Temperature; D014025:Titanium / Q000737:chemistry* / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: C521516:4-((pyridin-4-yl)vinyl)catechol; C521517:4-((quinolin-4-yl)vinyl)catechol; D002396:Catechols; D004396:Coloring Agents; D011725:Pyridines; D011804:Quinolines; C009495:titanium dioxide; D014025:Titanium; C034221:catechol