Composition‐Tuned Wide Bandgap Perovskites: From Grain Engineering to Stability and Performance Improvement

Abstract

Wide bandgap (WB) organic-inorganic hybrid perovskites (OIHPs) with a bandgap ranging between 1.7 and 2.0 eV have shown great potential to improve the efficiency of single-junction silicon or thin-film solar cells by forming a tandem structure with one of these cells or with a narrow bandgap perovskite cell. However, WB-OIHPs suffer from a large opencircuit voltage (V oc ) deficit in photovoltaic devices, which is associated with the phase segregation of the materials under light illumination. In this work the photoinstability is demonstrated and V oc loss can be addressed by combining grain crystallization and grain boundary passivation, achieved simultaneously through tuning of perovskite precursor composition. Using FA 0.17 Cs 0.83 PbI 3-x Br x (x = 0.8, 1.2 1.5, and 1.8), with a varied bandgap from 1.72 to 1.93 eV, as the model system it is illustrated how precursor additive Pb(SCN) 2 should be matched with a proper ratio of FAX (I and Br) to realize large grains with defect-healed grain boundaries. The optimized WB-OIHPs show good photostability at both room-temperature and elevated temperature. Moreover, the corresponding solar cells exhibit excellent photovoltaic performances with the champion V oc /stabilized power output efficiency reaching 1.244 V/18.60%, 1.284 V/16.51%, 1.296 V/15.01%, and 1.312 V/14.35% for WB-OIHPs with x = 0.8, 1.2, 1.5, and 1.8, respectively.

In situ recombination junction between p-Si and TiO 2 enables high-efficiency monolithic perovskite/Si tandem cells

“…For both 4-T and 2-T Si tandems, a bandgap of ~1.7 to 1.8 eV is expected to yield higher cell voltages ( 21 ), all other things being equal, than the 1.63-eV bandgap material used herein. At present, the high bandgap perovskites show a greater difference between the bandgap and cell open-circuit voltage ( V oc ) than the more optimized lower bandgap compositions ( 7 , 22 , 23 ), mitigating the potential gains in voltage. Layer thicknesses of ~120 and ~50 nm ( 22 ) were used for the organic hole–selective layers (Spiro-OMeTAD and PTAA, respectively).…”

Optical Absorption‐Based In Situ Characterization of Halide Perovskites

“…Reproduced with permission. [100] Copyright 2018, Wiley-VCH. c) PL intensity change over time under different atmospheric conditions.…”

“…[99] Moreover, via continuous PL monitoring they found that halide segregation can be suppressed by controlling the light distribution or the defect density in the film. [99] Zhou et al [100] compared PL intensity change over time in wide-bandgap Cs 0.17 FA 0.83 PbI 3-x Br x (x = 0.8, 1.2, 1.5, and 1.8)…”

“…A synergistic effect between larger grain size, reduced number of impurities, and passivated grain boundaries was suggested to explain superior photostability. [100] In another example, improved photostability in CsPbI 2 Br was found using a functionalized cathode interlayer and was explained by passivated electronic surface trap states. [103] Also the suppression of ion migration using oxygen to passivate halide vacancies has been shown.…”

Understanding macroscale functionality of metal halide perovskites in terms of nanoscale heterogeneities

“…(b) Reprinted with permission from [62]. Copyright 2017 Elsevier Inc. (c) prepared from data published in[53,57,69,72,104,105].…”