Recombination in SnO₂-Based Quantum Dots Sensitized Solar Cells: The Role of Surface States

Abstract

Tin oxide (SnO 2 ) is one of the most promising electron transporters to further enhance the performance of quantum dots sensitized solar cells (QDSCs). Unfortunately, the performance of SnO 2 -based QDSCs is still poor. It was observed that surface modification toward a SnO 2 photoelectrode such as a TiCl 4 treatment is crucial to dramatically increase the performance of the devices. However, the mechanism of the TiCl 4 treatment remains poorly understood.Here, systematic studies on the photoelectrochemical properties of SnO 2 -based QDSCs were performed in order to clarify the mechanism by which the TiCl 4 treatment improves the performance of solar cells. Impendence spectroscopy results reveal that the photogenerated electrons transport in the porous SnO 2 network rather than the TiO 2 coating. Furthermore, a physical model considering the existence of monoenergetic surface states at the SnO 2 surface was used to simulate the behavior of chemical capacitance at various forward biases. The accordance between the decrease of the surface states and the recombination reduction clearly indicates that the surface states act as the recombination centers to influence the device performance, which can be well described by Marcus-Gerischer theory. These combined findings provide new understanding of the recombination mechanism of SnO 2 -based sensitized solar cells and guidelines for further improving the performance of this system.

Investigating Charge Transfer in Functionalized Mesoporous EISA–SnO2 Films

“…These observations are in line with several reports highlighting the role of the surface localized states in the faster recombination rates in dye-sensitized solar cells made of nanoparticulate films of SnO 2 as compared to those made of TiO 2 . [16][17][18] In the present work, we moreover demonstrate that the α value is independent of the pH, a result which indicates that the low-energy surface states distribution follow the same pH-dependence as for the conduction band potential.…”

“…18 It is commonly assumed that these surface states are energetically located below the The 250-nm-thick EISA-SnO 2 electrodes were chemically functionalized by FMN and OsP (see Scheme S1 for molecular structures) through chemisorption of these compounds onto the metal oxide surface (on account of the presence of an organophosphorous anchoring group, the FMN and OsP compounds are able to strongly chemisorb onto the SnO 2 surface through a similar heterocondensation reaction than that previously demonstrated at ITO surfaces 29 ). These two molecules were selected because of (i) their intense redox-dependent visible absorption features Consequently, CVAs and DCVAs allow for a more specific and accurate monitoring of electron transfer reactions with adsorbed redox chromophores than CVs, for which the huge capacitive contribution at negative potentials tends to mask the faradaic response.…”

Quantum dot sensitized solar cell: Recent advances and future perspectives in photoanode

“…Efficiency is increased from 3.03% to 4.15% due to structural advantage of MD-THS. Huang et al modified surface of SnO 2 with TiCl 4 treatment to enhance photovoltaic performance of SnO 2 /TiCl 4 /PbS/CdS photoanode [98] (Fig. 13).…”

“…Because of effective electron transportation Reprinted with permission from Ref. [98]. Copyright (2013) American Chemical Society.…”

Study on negative incident photon-to-electron conversion efficiency of quantum dot-sensitized solar cells

“…F-doped SnO 2 (FTO) glasses (Nippon Sheet Glass; sheet resistance: 15 /square) were used for preparing both photoanodes and counter electrodes. First, TiO 2 and SnO 2 mesoporous films 13,14 were prepared for loading QDs, respectively, followed by TiCl 4 treatment. Subsequently, two kinds of QDs, CdS, 15 and PbS, 14,16 were assembled on the photoanode film by the successive ionic layer adsorption and reaction (SILAR) technique.…”