Understanding the origin of defect states, their nature, and effects on metal halide perovskite solar cells

Engineered 3D perovskite materials are promising candidates for high-efficiency solar cells, having already exceeded Copper indium gallium selenide (CIGS) and Cadmiun Telluride (CdTe) based single-junction cells and trailing only GaAs and Si. Nevertheless, their external luminescence quantum efficiency is modest (<5%) owing to high defect density, which plays an important role in charge trapping and recombination mechanisms for photogenerated carriers. Here, we review and attempt to formulate the rationale for possible types of defect formation and origin of defect core structure that largely deteriorate the 'optoelectronic quality' of perovskite materials and devices. The impact of these imperfections, which range from native 'point defects' to 'higher dimensional defects,' on solar cell efficiency is summarized and investigated. We observed that optoelectronic properties are limited at amorphous grain boundary fusion and transcend at heterojunctions, owing to 'microstructure' related defects. We highlight the intruding effects of 'defect migration' as it imposes unfavorable band alignment, interfacial chemical reactions, material phase separation, and J-V hysteresis. The ambiguous disparity in point defects behavior either at bulk or interface, and stoichiometric adjustment induced–tunned defect formation energies, are analyzed too. Our study emphasizes origin of distinct defects in perovskite and prominence of the acute need to advance the consensus in this exigent challenge.