Recent progress in fundamental understanding of halide perovskite semiconductors

The rapid progress in the field of organic–inorganic halide perovskite (OIHP) has led to not only >24% power conversion efficiency for photovoltaics, but also provided breakthroughs in processing of materials with tailored functional behavior. This ability to design and synthesize engineered OIHP materials has opened the possibility to develop various other optoelectronic applications. In addition to that of photovoltaics, this includes photodetector, laser, light emitting diode, X-ray and gamma detector, photocatalyst, memory, transducer, transistor, and more. At this stage, the emphasis is on fundamental understanding of the underlying physics and chemistry of OIHP materials, which will assist the evaluation of device performance and provide explanations for some of the contradictory results reported in literature. This review discusses the theoretical and experimental analysis of the OIHP materials reported from various sources and considers the chemical and structural origin of their unique optoelectronic properties, correlated microstructures, and newly discovered extraordinary properties. In the first few sections, we summarize and discuss the crystallography, chemical bonding, and substitutional effects, followed by the discussion of correlated photophysics including the optical, electronic, excitonic, charge transport, and ion migration characteristics. Next, we revisit and discuss the in-depth behavior of films with unique defect structure, structural disorder, morphology, and crystallization thermodynamics. Novel thermal-electrical-optical properties including ferroelectricity, hot-carrier contribution, spin-orbit coupling effect, terahertz time response, edge-state discovery, etc., are rationalized considering the results debated in the community. We elaborate on the opportunities and challenges regarding stability, toxicity, and hysteresis. The viewpoint on commercialization of OIHP based solar module is presented with the goal of identifying near-term opportunities. Throughout this review, the overarching goal is to provide a simplified explanation for the complex physical effects and mechanisms, underlying interconnections between different mechanisms, uncertainties reported in literature, and recent important theoretical and experimental discoveries.