Precursor Impurity Control for Stable Perovskite Tandem Photovoltaic Modules

Halide perovskites are a very promising technology to offer higher-power photovoltaics at low cost. Solar cells based on perovskites with >33% power conversion efficiency have been demonstrated, which would provide a higher power-to-weight ratio than conventional Silicon panels at similar costs. Such panels would fulfill a critical need from the US Army for power generation in portable or easily deployable arrays that will function under a range of environments. However, their operational stability is still considered to be lacking as compared to incumbent solar technologies, hindering commercialization. In our STTR Phase I, we demonstrated two critical aspects of durability for perovskite photovoltaics. Firstly, we showed that impurities in perovskite precursor materials can make the difference between cells that are stable enough for 25+ years of operation, and those that fail after a couple of years. The exact species and concentrations of impurity that can cause problems remain to be identified. Precursor purity also strongly affects cost, so understanding purity requirements will be critical to achieving both the stability and the price points relevant to commercialization.Secondly, we identified a significant loss in stability between small, unpackaged cells and larger, glass-packaged minimodules - the configuration in which modules are deployed. This loss resulted in much lower stabilities for packaged minimodules in combined environmental testing than we would expect, making them not durable enough for years of operation in the field, despite attaining high initial power conversion efficiencies.In this project we bring together expertise in analytical technique development and characterization (UCSD) and perovskite device fabrication (Swift). We will carry out thorough studies to solve both of the issues identified above. By intentionally adding impurities into ultra-pure starting materials and building devices, we will establish impurity profile specifications for incoming precursors by quantifying which species and what concentrations cause problems with device stability. In order to understand the nature of degradation processes unique to packaged perovskite minimodules, we will develop both new analytical techniques and new module designs, specific to probing the perovskite-based materials both during degradation and post-mortem. By measuring and understanding the degradation processes, we will then develop strategies to mitigate them, which will likely be based on module engineering or material choices. We will build larger modules (>1000cm2) to prove durability in field-relevant form factors, and subject modules to a suite of combined environmental tests. We will use combined fielding, experimental and modeling approaches to demonstrate perovskite tandem modules with lifetimes of >8000h (1 year) under 1 sun, in any of the 11 climatic operating conditions specified in AR 70-387 - ranging from extreme cold to hot humid conditions