Charge Transfer from Methylammonium Lead Iodide Perovskite to Organic Transport Materials: Efficiencies, Transfer Rates, and Interfacial Recombination

Abstract

IntroductionSolar cells employing metal halide perovskites as light absorbers have undergone a tremendous development over the past years, resulting in photovoltaic devices with record efficiencies exceeding 22%. [1][2][3] The impressive progress in device efficiency is mainly due to (i) optimizing experimental procedures to obtain perovskite materials with improved crystallinity, (ii) adjusting the perovskite composition, and (iii) investigating different transport materials. However, it remains a major Perovskite-based photovoltaics have been rapidly developed, with record power conversion efficiencies now exceeding 22%. In order to rationally design efficient and stable perovskite solar cells, it is important to understand not only charge trapping and recombination events, but also processes occurring at the perovskite/transport material (TM) interface, such as charge transfer and interfacial recombination. In this work, time-resolved microwave conductivity measurements are performed to investigate these interfacial processes for methylammonium lead iodide and various state-of-the-art organic TMs. A global kinetic model is developed, which accurately describes both the dynamics of excess charges in the perovskite layer and transfer to chargespecific TMs. The authors conclude that for state-of-the-art materials, such as Spiro-OMeTAD and PCBM, the charge extraction efficiency is not significantly affected by intra-band gap traps for trap densities under 10 15 cm -3 . Finally, the transfer rates to C60, PCBM, EDOT-OMeTPA, and Spiro-OMeTAD are sufficient to outcompete second order recombination under excitation densities representative for illumination by AM1.5.

Efficient Perovskite Solar Cells over a Broad Temperature Window: The Role of the Charge Carrier Extraction

“…Recent work by Huang and co-workers indicated that thermal annealing of [60]PCBM could passivate traps in the perovskite film. [23] In our case, the thermal treatment of [24,25] The extent of the PL quenching by all the EELs is similar at high and low temperature, showing that the electron transfer occurs with similar efficiency at different temperatures. At low temperature, the enhanced PL emission of the perovskite layer is an indication of higher band-to-band recombination of the free electrons and holes, lower nonradiative recombination due to the deactivated traps and lower photon scattering ( Figure S10, Supporting Information).…”

How To Quantify the Efficiency Potential of Neat Perovskite Films: Perovskite Semiconductors with an Implied Efficiency Exceeding 28%

“…[ 10 ] As with many emerging photovoltaic technologies, a major focus of the research community has been trying to understand the origin of open‐circuit voltage losses and a range of different measurement techniques have been proposed to decouple, for example, the contribution of interfacial and bulk recombination on the V OC of the cell. [ 11–19 ] These include electrical [ 19 ] and all‐optical transient measurements such as pump‐probe techniques [ 14–16,20,21 ] ; moreover all‐electrical measurements, for example, impedance spectroscopy [ 15,17,20–22 ] and optical measurements in steady‐state such as photoluminescence spectroscopy. [ 11–13 ] Other attempts have been made to explain the dominant recombination mechanism via the ideality factor ( n ID ) of the complete cell, [ 11,23–26 ] however with somewhat limited success considering the difficulty of describing multiple parallel recombination processes in a cell by a single parameter.…”

Direct Observation of Charge Injection From CH3NH3PbI3−xClx to Organic Semiconductors Monitored With sub‐ps Transient Absorption Spectroscopy

“…In most of the mentioned reports the injection is observed indirectly by monitoring changes of the TAS signals characteristic for the perovskite layer. The temporal evolution of these signals can be influenced by additional factors, such as film quality and morphology or interfacial recombination . Direct observation of charge carrier injection by detecting spectral signatures caused by the injected carriers in the adjacent contact material is therefore highly desirable.…”