Dipolar cations confer defect tolerance in wide-bandgap metal halide perovskites

Hairen Tan,Eduard Fron,Junghwan Kim,Furui Tan,Haifeng Yuan,Mark Asta,Bin Sun,Makhsud I Saidaminov,Oleksandr Voznyy,Fanglin Che,Mingyang Wei,Danny Broberg,Petar Todorović,Zhenyu Yang,Taotao Zhuang,Grant Walters,Zhiqin Liang,Edward H Sargent,Yicheng Zhao

doi:10.1038/s41467-018-05531-8

Abstract

Efficient wide-bandgap perovskite solar cells (PSCs) enable high-efficiency tandem photovoltaics when combined with crystalline silicon and other low-bandgap absorbers. However, wide-bandgap PSCs today exhibit performance far inferior to that of sub-1.6-eV bandgap PSCs due to their tendency to form a high density of deep traps. Here, we show that healing the deep traps in wide-bandgap perovskites—in effect, increasing the defect tolerance via cation engineering—enables further performance improvements in PSCs. We achieve a stabilized power conversion efficiency of 20.7% for 1.65-eV bandgap PSCs by incorporating dipolar cations, with a high open-circuit voltage of 1.22 V and a fill factor exceeding 80%. We also obtain a stabilized efficiency of 19.1% for 1.74-eV bandgap PSCs with a high open-circuit voltage of 1.25 V. From density functional theory calculations, we find that the presence and reorientation of the dipolar cation in mixed cation–halide perovskites heals the defects that introduce deep trap states.

Highlights

Efficient wide-bandgap perovskite solar cells (PSCs) enable high-efficiency tandem photovoltaics when combined with crystalline silicon and other low-bandgap absorbers
Our density functional theory (DFT) studies reveal that the incorporation and reorientation of the dipolar MA cation in mixed perovskites offer the potential to heal the defects that introduce deep trap states in CsFA perovskite
RSRH can be reduced in CsMAFA perovskite by decreasing the capture cross-section of traps due to the screening of defects by MA dipoles, or by reducing in-gap trap density or rendering shallower trap levels

Summary

Introduction

Efficient wide-bandgap perovskite solar cells (PSCs) enable high-efficiency tandem photovoltaics when combined with crystalline silicon and other low-bandgap absorbers. 6 Department of Chemistry, KU Leuven, Wide-bandgap perovskite solar cells (PSCs) enable efficient monolithic tandem devices with crystalline silicon (c-Si) and other leading low-bandgap materials because of their high open-circuit voltage (Voc) and tunable bandgaps (Eg)[1,2,3,4,5,6,7]. We reasoned that healing the deep traps in perovskite absorber—in effect, increasing the defect tolerance22,23— could enable further performance improvements in widebandgap PSCs. Sub-1.6 eV bandgap PSC strategies indicate that A-site cation compositional engineering is crucial to achieve the bestperforming devices[18,20,24,25].

Methods

Results

Conclusion