Effect of Grain Size and Interface Engineering on the Photovoltaic Performance and Stability of Perovskite Solar Cells

Organic-inorganic halide perovskite solar cells (PSCs) have grown rapidly in recent years due to their outstanding optoelectronic properties, high efficiency, and low-cost. However, this emerging solar cell technology is experiencing some challenges such as defects, hysteresis, and long-term stability, which need to be addressed in order to make it commercially available. This dissertation aims to assist in overcoming some of the barriers and is therefore important to the field of perovskite solar cells. Initially, this dissertation focuses on investigating the role of grain interiors (GIs) and grain boundaries (GBs) of perovskite film using chemically, spatially, and temporally resolved measurements at the nanoscale level. It is shown that, the GBs are defective with deeper defect levels and are unfavorable to the high performance of perovskite solar cells. Therefore, larger grain perovskite film can be considered as a plausible solution for better quality perovskite films. This work leads to a novel deconvoluted PL approach to determine the charge carrier dynamics of the GI and the GB of the perovskite film. We have quantitatively demonstrated that the charge carrier dynamics of the GI and GB can be analyzed from the ordered and disordered phase of the asymmetric PL spectrum observed in the perovskite film. This deconvoluted PL approach is simple, rapid, non-destructive, and requires no sample preparation compared with the currently available nanoscale characterization measurements. Subsequently, this dissertation describes the interface defect passivation between perovskite and the electron transport layer (ETL). To address this, a novel thin film of PCBM/carbon was introduced as ETL in the device architecture, which reduces the interface defects and increases the conductivity compared with that of the competitive ETL of PCBM/C60. Moreover, carbon is abundant in nature and the use of carbon in perovskite solar cells will reduce the manufacturing cost. Finally, the limitation of the air instability of perovskite film is investigated. For that, an in-depth study of degradation pathways of the perovskite film in air was performed using optical, crystallographic, morphological, and mechanical measurements. Based on this study, we suggest the modification of perovskite device architecture to improve the stability of perovskite solar cells in air.