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

Perovskite Solar Cell Performance Boosted by Regulating the Ion Migration and Charge Transport Dynamics via Dual-Interface Modification of Electron Transport Layer

Engineering the buried interfaces of perovskite solar cells (PSCs) is crucial for optimizing the device performance. We herein report a novel strategy by modifying the ETL-FTO interface with MgO, as well as the interface between the perovskite layer (PVKL) and the SnO2 electron transfer layer (ETL) with formamidine bromide (FABr). The dual-interface ETL engineering substantially improved the photoelectric conversion efficiency (19.62 → 22.04%) and suppressed the hysteresis index (14.98 → 1.09%). The structure-activity relationship was explored by using transient photoelectric and time-of-flight secondary-ion mass spectroscopic analyses. It was found that the FABr treatment enhanced the PVKL crystallinity and the PVKL-ETL interaction and that the MgO modification dramatically retarded the ion migration, which together optimized the ETL function. The mechanism underlying the influence of ion distribution on the dynamics of ions and free carriers is discussed, which may be helpful for the rational design of high-performance PSCs.

Extraction technique of trap states based on transient photo-voltage measurement

This article puts forward a technique for extracting the density of trap states (DOS_T) distribution based on the transient photo-voltage (TPV) measurement result. We prove that when the TPV result is linear, the DOS_T distribution is exponential type and vice versa. Compared to the approach based on the space charge limited current measurement, the method given in this paper has the advantage of requiring less calculation. The results obtained by our method provides a guidance for preparing less trap states solar cells.

Trap-Limited Dynamics of Excited Carriers and Interpretation of the Photoluminescence Decay Kinetics in Metal Halide Perovskites

Interpretation of the photoluminescence (PL) decay kinetics in metal halide perovskites (MHPs) is extremely important for understanding the mechanisms and control of charge recombination in these promising photovoltaic and optoelectronic materials. In this work, we give a review of current models describing the PL decay kinetics in MHP layers and nanocrystals with particular attention to the interpretation of long-lived PL decay components (hundreds of nanoseconds to microseconds). First, we analyze phenomenological photophysical models based on the rate equations, which describe the charge carrier recombination in MHP layers as an exclusively intrinsic bulk process. An important role of the carrier diffusion and nonradiative recombination on the layer surfaces is then discussed. A recently published approach is then analyzed, in the framework of which the observed long-lived components of PL decay kinetics in MHP nanocrystals are described in terms of the delayed luminescence mechanism arising due to the processes of multiple trapping and detrapping of carriers by shallow nonquenching traps. The possible origin of the shallow traps and perspectives to include the carrier trapping and detrapping processes in a model describing PL kinetics in MHP layers are discussed.