Nanoscale Spatial Realization of Grain Boundary Defects And its Passivation In Perovskite Solar Cells

Perovskite solar cells (PSCs) have seen significant improvement in photovoltaic performance in recent days. However, the performance of PSCs is limited by the defects present at grain boundaries (GB). The study adapted here discusses the nanoscale spatial realization of grain boundary defects and its passivation in perovskite solar cells. Conventional MAPbI3 and state- of-the-art Cs5(MA0.17FA0.83)95Pb(I0.83Br0.17)3-FAMACs perovskite GBs were studied in detail using atomic force microscopy. The density of trap states calculation by kelvin probe force microscopy (KPFM) shows that FAMACs perovskites have lower defects at GB compared with MAPbI3 perovskites. This improvement is caused by the less activation energy of the point defects in FAMACs due to mixing of cations and anions in perovskite structure compared with MAPbI3 perovskites. FAMACs perovskite GBs are less dominated by the defect ion migration evident from the negligible local dark-current hysteresis at GBs. To further passivate defects at the GB, FAMACs perovskite was post-treated by using an organic halide salt named phenylhydrazinium iodide (PHI). Defects analysis and passivation at GB of FAMACs perovskite were evaluated using atomic force microscopy technique through mapping of carrier recombination lifetime (τr), transport time (τt) and diffusion length (LD). These spatially resolved charge carrier dynamics parameters reveal substantial variations at GB of control and passivated perovskites. Defects analysis and passivation at GB of FAMACs perovskite through charge carrier dynamics nanoscale mapping, KPFM and CAFM demonstrate that optimized concentration of PHI can passivates the positively charged defects and significantly improves charge carrier dynamics at GB compared to control sample. This improvement in nanoscale charge transport in passivated FAMACs gives a PCE of ~20% whereas MAPbI3 and non-passivated FAMACs perovskites show ~17% and ~ 18% PCE, respectively. This clearly indicates that GB passivation in FAMACs reduces the positively charged defects and gives champion PCE of ~20%

Rapid and Low-Temperature Processing of Mesoporous and Nanocrystalline TiO2 Film Using Microwave Irradiation

Nanoporous (np)-TiO2 films have multiple applications, including dye-sensitized and perovskite solar cells. However, preparation of np-TiO2 films on transparent conductive oxide-coated surfaces (e.g., fluorine doped tin oxide (FTO)) requires high-temperature sintering (450–500 °C) for at least 30–60 min in a conventional oven. Here, we introduce a novel technique to rapidly produce np-TiO2 films on FTO-coated glass substrates via microwave (MW) irradiation. np-TiO2 films were sintered on FTO-glass substrates in less than 10 min at temperatures less than 260 °C using an optimized MW irradiation program and a simple MW attenuation technique. Significantly, cracking of FTO-coated glass substrates was avoided during MW irradiation, which was a limiting problem in previous studies. MW-developed films were evaluated with UV–vis absorption spectrophotometry, Raman spectroscopy, X-ray diffraction, and atomic force microscopy, with MW-developed films ( \u3e4 min) producing essentially identical characteristics as conventionally annealed films. Dye-sensitized solar cells (DSSCs) fabricated with MW-developed films (8 min) demonstrated an overall power conversion efficiency of 7.16% as compared to 7.04% for conventionally-fabricated DSSCs. This rapid and low-temperature sintering technique saves time and energy and may also pave the way for deposition of np-TiO2 films on plastic-based substrates