Photovoltaic & Optoelectronic Device Group

Abstract:

Perovskite photovoltaics advance rapidly, but questions remain regarding point defects: while experiments have detected the presence of electrically active defects no experimentally confirmed microscopic identifications have been reported. Here we identify lead monovacancy (VPb) defects in MAPbI3 (MA = CH3NH3+) using positron annihilation lifetime spectroscopy with the aid of density functional theory. Experiments on thin film and single crystal samples all exhibited dominant positron trapping to lead vacancy defects, and a minimum defect density of ~3 7 1015 cm−3 was determined. There was also evidence of trapping at the vacancy complex (VPbVI)− in a minority of samples, but no trapping to MA-ion vacancies was observed. Our experimental results support the predictions of other first-principles studies that deep level, hole trapping, VPb2−, point defects are one of the most stable defects in MAPbI3. This direct detection and identification of a deep level native defect in a halide perovskite, at technologically relevant concentrations, will enable further investigation of defect driven mechanisms

Abstract:

Hybrid lead-halide perovskites are widely used in a variety of optoelectronic applications, including perovskite solar cells (PSCs), perovskite light-emitting diodes (PeLEDs), perovskite photodetectors (PPDs), and scintillators. Recently, it was demonstrated that bulky organic cations (BOCs) can be used as surface passivation agents to fine-tune the dimensionality of lead-halide perovskites, making it possible to tailor their optoelectronic properties and enhance their stability. This special feature has further improved the commercialization potential of perovskite-based optoelectronic devices. In this article, we provide a comprehensive review of the recent progress in low/multidimensional perovskites prepared via BOC treatment and their performance in various optoelectronic devices. We begin by introducing the special features and fundamental properties of lead-halide perovskites with different dimensionalities and the working mechanism of BOC treatments. Thereafter, we separately highlight and discuss the device architecture and performance breakthroughs of BOC-treated perovskites in (i) PSCs, (ii) PeLEDs, and (iii) PPDs and scintillators, emphasizing works published from 2018 till now. For each application, the influence of BOC treatments on device performance and stability is discussed. At the end of this review, we provide our insights on future challenges and commercialization opportunities for BOC-treated perovskites in the field of optoelectronics.