Charge Carrier Recombination Dynamics in Optimized Composition of Sn versus Pb based Perovskite Solar Cells.
Shivam Singh a, Dinesh Kabra a
a IIT Indian Institute of Technology Bombay, Department Physics, India
Proceedings of SUNRISE September Symposium 2021 ‘Powering Green Recovery’ (SUNRISEIII)
Online, Spain, 2021 September 20th - 22nd
Organizers: Hari Upadhyaya, Adrian Walters, James Durrant, Sara Walters and Georgia Bevan
Invited Speaker, Shivam Singh, presentation 026
Publication date: 14th September 2021

The energy bandgaps of Pb halide perovskites are higher than the optimal bandgap required for single junction solar cells, governed by the Shockley–Queisser (SQ) radiative limit. The pure Sn and Pb-Sn mixed based perovskites have drawn significant attention due to their ability to lead to lower bandgaps and opens a new door for all perovskite tandem application. There is continuous progress towards the rapid improvement in the power conversion efficiency of Sn and Pb-Sn mixed based PSCs. Along with efforts for efficiency, it is worth analysing the in-depth recombination dynamics for further development of Sn based PSCs. Lower bimolecular recombination rate constant (k) is often attributed for the high performance of PSCs. Herein, we study the role of ‘B’ cation in charge carrier recombination dynamics (CCRD) of ABX3 (A= MA+, FA+, Cs+; B = Pb2+, Sn2+ & X = I-) based PSCs. We fabricated p-i-n configuration based FA0.95Cs0.05PbI3 (pure Pb), MA0.20FA0.75Cs0.05SnI3 (pure Sn) and (MAPbI3)0.4 (FASnI3)0.6 (Pb–Sn mixed) PSCs and compare the CCRD of all the three PSCs. We optimized the Sn based perovskite thin film (pure Sn) in terms of moisture and thermal stability in order to minimize the error due to perovskite degradation. We note that despite having lower open-circuit voltage (VOC), pure Sn based PSC shows lower k than that of Pb-Sn mixed and pure Pb based PSCs, which is a contradictory result. This slow relaxation lifetime of the charge carrier in Sn based PSCs can be correlated to recombination through the defect states without introducing the quasi-Fermi-level splitting. Furthermore, our results suggest that the rate law of charge carrier decay has nonlinear dependence of k on n in Sn based PSCs, whereas it is linear in other two cases.

The authors would like to acknowledge the financial support granted by the Ministry of New and Renewable Energy, India (16MNRE002). This work was also partially supported by the UKRI Global Challenge Research Fund Project, SUNRISE (EP/P032591/1). The authors also acknowledge the support of the National Centre for Photovoltaic Research and Education (NCPRE), IIT Bombay, for deposition facility and characterization. The authors also acknowledge the ESCA, Central Facility, IIT Bombay, for UPS measurement. The authors also acknowledge Pilkington for transparent conductive oxide electrodes.

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