| Solar photovoltaics (PV) offer a sustainable solution to the daunting challenge of meeting the global energy demand. Perovskite solar cells, whose high efficiencies are attainable via low-cost and high-throughput solution processing, are an emerging technology that has captivated the PV research community. Further advances in efficiency are limited by the abundant interfaces that make up these polycrystalline devices. Important issues in perovskite device operation, such as instability and hysteresis, arise from perovskites' ionic nature, and need to be addressed for this technology to fulfill its potential.;In this thesis, I explore interfaces within perovskite devices: grain boundaries, and electron- and hole-extraction junctions. With the aid of density functional theory (DFT) simulations and nano-probe characterization, I provide insight into the origins of defect formation and hysteresis. By leveraging these findings, I demonstrate control of film growth conditions and interface materials chemistry to create new device architectures with improved performance. The DFT-based analysis of defect formation energies identifies the key defects (Pb atom substituted by I, known as antisites) and indicates that films grown under iodine-rich conditions are prone to forming deep electronic traps. This finding motivated my exploration of a new precursor (anhydrate lead acetate) for device-quality films.;I then report the first perovskite-PCBM hybrid solid. Here, I find that PCBM, when it infiltrates throughout the grain boundaries and electron-extraction interfaces, suppresses hysteresis in devices. Materials characterization and DFT simulations reveal the PCBM-perovskite interaction: the PCBM passivates the key defects during the perovskite self-assembly. Using conductive AFM, I reveal the memristive properties of perovskite films and identify the major origin of hysteresis as ion, especially halide, migration.;I close by developing the first crosslinked hole-extraction top contact with the goal of obviating degradation of the underlying perovskite. A remote-doping strategy introduces the needed hole conductivity. The new top contact produces an insoluble and heat-resistant protecting interlayer that is band-aligned with the perovskite. The resultant family of devices is hysteresis-free, with fill factors exceeding 80% and resilience to thermal stresses that exceed 100?C, conditions under which conventionally-contacted devices fail. This top contact methodology also paves the way for building multi-junction devices on top of the perovskite cell. I close this work by offering a roadmap for future improvements in perovskite photovoltaics. |
