Interfacial Engineering for Quantum‐Dot‐Sensitized Solar Cells

Abstract

Quantum-dot-sensitized solar cells (QDSCs) are promising solar-energy-conversion devices, as low-cost alternatives to the prevailing photovoltaic technologies. Compared with molecular dyes, nanocrystalline quantum dot (QD) light absorbers exhibit higher molar extinction coefficients and a tunable photoresponse. However, the power-conversion efficiencies (PCEs) of QDSCs are generally below 9.5 %, far behind their molecular sensitizer counterparts (up to 13 %). These low PCEs have been attributed to a large free-energy loss during sensitizer regeneration, energy loss during the charge-carrier transport and transfer processes, and inefficient charge separation at the QD/electrolyte interfaces, and various interfacial engineering strategies for enhancing the PCE and cell stability have been reported. Herein, we review recent progress in the interfacial engineering of QDSCs and discuss future prospects for the development of highly efficient and stable QDSCs.

Interface Engineering in Quantum-Dot-Sensitized Solar Cells

“…78,80 Although the polysulfide electrolyte has a superior hole-extraction ability, the devices fabricated with this electrolyte suffer from lower V oc and FF when compared to DSSC as a result of its negative redox potential (−0.67 V vs Ag/ AgCl) and sluggish interfacial charge transfer at the CE and electrolyte interface. 81 Therefore, the replacement of the polysulfide electrolyte with some other electrolyte, e.g., cobalt complexes which have a more positive redox potential can be beneficial, although the device efficiency could not be improved due to severe photocorrosion and fast charge recombination.…”

“…The problems were solved when the S 2– /S n 2– redox electrolyte was introduced at the expense of lowering the driving potential and thus the conversion efficiency . The redox couple in the electrolyte collects holes from the photoanode (TiO 2 /QDs) by the mechanisms The reverse reaction happens at the electrolyte/CE interface where the oxidized species (S n 2– ions) are converted back to S 2– by taking electrons from the CE: Several modifications such as the inclusion of additives and structural modification have been employed to improve the QDSSC performance. , Although the polysulfide electrolyte has a superior hole-extraction ability, the devices fabricated with this electrolyte suffer from lower V oc and FF when compared to DSSC as a result of its negative redox potential (−0.67 V vs Ag/AgCl) and sluggish interfacial charge transfer at the CE and electrolyte interface . Therefore, the replacement of the polysulfide electrolyte with some other electrolyte, e.g., cobalt complexes which have a more positive redox potential can be beneficial, although the device efficiency could not be improved due to severe photocorrosion and fast charge recombination.…”

ZnSxSe1–x Alloy Passivation Layer for High-Efficiency Quantum-Dot-Sensitized Solar Cells

“…The development of QD light-harvesting materials as well as the counter electrode materials has promoted the development of QDSCs in recent years. − Beyond that, one of the main reasons limiting the efficiency improvement of QDSCs is the severe charge recombination loss in the device. , The interfacial charge recombination problem is particularly serious in QDSCs. ,− The defect trap states in QDs are charge recombination centers in QDSCs. , However, although the indirect QD deposition approach on TiO 2 surface with use of presynthesized QDs has delivered a higher PCE compared to the direct deposition approach, the coverage fraction of QDs on the surface of TiO 2 substrate is still low for this indirect deposition method, and the highest surface coverage reported so far is only 34% . That is to say, there is a large portion of the TiO 2 substrate exposed to the electrolyte directly, increasing the probability of electron leakage from TiO 2 to electrolyte .…”

Enhanced light harvesting and electron collection in quantum dot sensitized solar cells by TiO2 passivation on ZnO nanorod arrays

“…These include: the great diversity of QDs, ease of fabrication, high stability in different surroundings (water or oxygen), and inexpensive production costs [1][2][3]. QDSCs comprise five main components: a transparent charge collector (typically fluorine doped tin oxide (FTO) or indium tin oxide (ITO)), a mesoporous metal oxide semiconductor (MOS) film serving as the photoanode, QDs attached on the surface of MOS film as photo-sensitizer, a liquid or solid-state electrolyte as a hole transporting media, and a counter electrode with electrocatalytic activity [4]. The mesoporous photoanode, as a support matrix, plays a key role in determining the surface area available for loading of QDs for light harvesting, and in influencing charge transfer from the QDs to the electrodes.…”