Improving the Efficiency, Stability, and Flexibility of Perovskite Solar Cells

Abstract

Solar cells are a renewable, clean alternative to fossil fuels. Silicon solar cells are used in about 90% of commercial modules. Despite having high efficiency and stability, silicon solar cells are costly and rigid. To produce an efficient, stable, cost-effective, and flexible module, different strategies have been explored. One strategy is photon upconversion, where multiple sub-bandgap photons can be converted into a single photon of higher energy, allowing it to be absorbed by the semiconductor of a solar cell. Another strategy is the cost-effective fabrication of efficient perovskite solar cells, composed of CH3NH3I and PbI2. Unlike silicon, the perovskite can be fabricated on top of flexible plastic substrates coated with transparent conductive metal oxide electrodes; however, the limit of its flexibility needs to be explored and improved for real-world applications. More importantly, the major barrier to the commercialization of perovskite solar cells is their instability when exposed to either high humidity or O2 and sunlight. Therefore, improving stability, while not sacrificing efficiency, is extremely important. In this thesis, different strategies are developed to fabricate such a multi-faceted solar cell. Plasmonics are used to enhance the quantum yield of the photon upconversion process. As another strategy, the inflexible metal oxide electrodes of perovskite devices are replaced by flexible polymer-based ones. Then, the intrinsic flexibility of the CH3NH3PbI3 layer is assessed by comparing the results of bending tests performed on a perovskite device and on a highly-flexible organic solar cell. Furthermore, the results of compositional engineering are shown, where partially replacing the CH3NH3+ cation with formamidinium is shown to improve the stability of the perovskite film. Following this, the possibility of completely eliminating CH3NH3+ from state-of-the-art devices is shown, resulting in improved stability and similar efficiencies.