Manipulate the Second Order Non-radiative Recombination Process in MAPbBr3 Perovskites
Jiashang Zhao a, Tom Savenije a
a Department of Chemical Engineering, Delft University of Technology (TU Delft), The Netherlands, Netherlands
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Poster, Jiashang Zhao, 228
Publication date: 20th April 2022

Nonradiative recombination (kR) of charge carriers is of crucial important factor result in energy losses in perovskite solar cells and other optoelectronic devices. An effective method of defect passivation is often used to reduce the trap density at surface or grain boundaries, leading to an suppression of kR. However, how does trap passivation affect the charge carrier dynamics in metal halide perovskite is still not fully understood. Here, the charge carrier recombination processes in MAPbBr3 with and without hypophosphorous acid (HPA)  are investigated in the temperature range from 300 K to 90 K by using time-resolved microwave conductivity (TRMC) and photoluminescence (PL) techniques. The introduction of HPA increases the average grain size by a factor of 3 and reduces the total concentration of the trap states by a factor of 10. From analysis of temperature (T) dependent TRMC in MAPbBr3, the second-order electron-hole recombination (keff) included both radiative (kR) and nonradiative (knR) parts is gradually decreased as lowering temperature in pristine MAPbBr3. While keff is substantially reduced and independent of T after passivation. PL spectra show the intensities of passivated MAPbBr3 are at least 2 times higher than that of pristine one at the entire T range. From these observations, we proposed a model presented an upward band bending with the Fermi level alignment at perovskite bulk and surface interface. From which an additional non-radiative recombination pathway (knR), electrons overcoming an energy barrier recombine with the holes in the trap states at the surface, only occurs in pristine MAPbBr3 film, apart from kR. This knR process might be thermally activated and results in a fast initial decay in TRMC at higher temperatures in pristine MAPbBr3.

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