New insights into electrolyte-component biased and transfer- and transport-limited charge recombination in dye-sensitized solar cells

Abstract

We carried out time-resolved charge extraction (TRCE) study on the charge recombination dynamics of open-circuit dye-sensitized solar cells (DSSCs) by examining the temporal evolution of electron density with varying the concentration of electrolyte component tert-butylpyridine (TBP).The charge recombination dynamics extracted from TRCE results exhibit distinctly different temporal behavior depending on the photovoltage or electron density. We proposed a theoretical model of electron density dependent charge recombination, which unifies the transport-and transfer-limited charge recombination mechanisms. This model, as rationalized by transient photovoltage (TPV) kinetics, can account well for the TRCE results. The relevance between electron transport and charge transfer in recombination process was unraveled, and the electron density dependent pathway of charge recombination was elucidated.

Multiple‐Trapping Model for the Charge Recombination Dynamics in Mesoporous‐Structured Perovskite Solar Cells

“…Figure 1s hows the ideal multiple-trapping assistedc harge recombination;h owever,m odificationsa re often required when describing real experiments. [36] If we add k ss in Equation (14), the modified k r -V ph relation is written as: [35] The reasonisascribed to the alternative recombination pathway at low voltage (i.e., the isoenergetic electrons transfer from surfacestate of the TiO 2 to the electrolyte acceptors), which cannot be described by multiple-trapping mechanism.…”

“…[34] Very recently,w er eported that surface-state-dominated charge recombination obeys the transfer-limited recombination process, which leads to as tationary rate constant k ss . [36] If we add k ss in Equation (14), the modified k r -V ph relation is written as:…”

Working area effects on the energetic distribution of trap states and charge dynamics of dye-sensitized solar cells

“…The surface traps are localized electronic states in the band gap and are physically located either at the TiO 2 surface or within a tunneling distance from the surface. 16 As the electrons trapped by surface states are intensely localized, the electron transfer from TiO 2 to electrolyte is slower, i.e., the recombination channel is faster. 20 A deeper DOS distribution indicates that more electrons are in deep trap states; thus, the electronic recombination rate of the large working area DSSC (T-2) is faster than that of the small working area cell (T-1).…”

“…This result highlights the importance of improving charge collection efficiency to achieve high-efficiency DSSCs with a large area. This improvement can be achieved by modifying the photoanode morphology, 15 electrolyte engineering, 16 as well as other approaches.…”

The Influence of Morphology and PbI2 on the Intrinsic Trap State Distribution in Perovskite Films Determined by Using Temperature‐Dependent Fluorescence Spectroscopy

“…[54,55] In recent years, we have reported that time-resolved charge extraction (TRCE) could act as another effective candidate to study quantitatively the DOS distribution in dye-sensitized solar cells, quantum-dot-sensitized solar cells, and perovskite solar cells. [56][57][58][59][60] However,asignificant limitation of these methods is that the tested system should be connected to as hort or open circuit,s ot hey are unable to investigate the trap states in intrinsic perovskite films without selected electrodes. In contrast, transient infrareda bsorption spectroscopy can be used to measure the DOS distribution of thin films, but it is not easy to identify the characteristic optical signals and the requirement of instrumentsa nd technology is relatively high.…”