Abstract
Photoinduced charge separation (PCS) plays an essential role in various solar energy conversions such as photovoltaic conversion in solar cells. Usually, PCS in solar cells occurs stepwise via solar energy absorption by light absorbers (dyes, inorganic semiconductors, etc.) and the subsequent charge transfer at heterogeneous interfaces. Unfortunately, this two-step PCS occurs with a relatively large amount of the energy loss (at least ca. 0.3 eV). Hence, the exploration of a new PCS mechanism to minimize the energy loss is a high-priority subject to realize efficient solar energy conversion. Interfacial charge-transfer transitions (ICTTs) enable direct PCS at heterogeneous interfaces without energy loss, in principle. Recently, several progresses have been reported for ICTT at organic-inorganic semiconductor interfaces by our group. First of all, new organic-metal oxide complexes have been developed with various organic and metal-oxide semiconductors for ICTT. Through the vigorous material development and fundamental research of ICTT, we successfully demonstrated efficient photovoltaic conversion due to ICTT for the first time. In addition, we revealed that the efficient photoelectric conversion results from the suppression of charge recombination, providing a theoretical guiding principle to control the charge recombination rate in the ICTT system. These results open up a way to the development of ICTT-based photovoltaic cells. Moreover, we showed the important role of ICTT in the reported efficient dye-sensitized solar cells (DSSCs) with carboxy-anchor dyes, particularly, in the solar energy absorption in the near IR region. This result indicates that the combination of dye sensitization and ICTT would lead to the further enhancement of the power conversion efficiency of DSSC. In this feature article, we review the recent progresses of ICTT and its application in solar cells.
Highlights
Photoinduced charge separation (PCS) at heterogeneous interfaces between electron-donating (D)and -accepting (A) substances play an important role in various solar energy conversions ranging from photovoltaic conversion in solar cells to photocatalytic reactions such as solar-to-fuel energy conversion
This result indicates that the combination of dye sensitization and Interfacial charge-transfer transitions (ICTTs) would lead to the further enhancement of the power conversion efficiency of dye-sensitized solar cells (DSSCs)
We briefly introduce the history of the fundamental research of ICTT
Summary
Photoinduced charge separation (PCS) at heterogeneous interfaces between electron-donating (D). Reported in 2000 and 2003 photovoltaic conversion due to ICTT in the TiO2 -AA surface complex and estimated IPCE to be ca. It was seen that ICTTs in the TiO2 -enediol surface complexes give rise to quite inefficient photovoltaic conversion with the low IPCE values. Since organic-inorganic semiconductor hybrids for ICTT were quite limited at that time, there had been no further progress on the photovoltaic conversion based on direct PCS until around 2010. We examined photovoltaic properties of ICTT in the TiO2 -TCNQ surface complex [50]
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