Role of the cation in hybrid organic-inorganic perovskite solar materials
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Climate change has renewed research into alternative power sources. One hot research topic is that of novel solar devices such as the hybrid inorganic-organic perovskite solar cell. Currently, hybrid perovskite solar cells are at 22.7% efficiency and are now exceeding all other thin film technology. The lone hurdle to wide spread adoption of hybrid perovskite solar cells remains thermal and water stability. Since the first reported perovskite solar cells using methylammonium lead iodide, researchers have been hard at work looking to address the stability issues. The use of different cations and the use of alloys of these cations have been proposed as solutions to the stability issues. One such alloy consisting of cesium, methylammonium and formamidinium is a leading candidate for commercialization of the perovskite solar cell. While the interactions of the lead cation and the halides are well understood, the role of the organic cation in the structure is not. This work examines the role of the cation in an alloy perovskite of cesium, methylammonium and formamidinium. This work uses SEM, XRD, XPS, AFM, KPFM, EDS, FTIR and IV measurements to highlight how the electronegativity, size and mass of the cations contribute to the resulting perovskite films in terms of solar characteristics, crystal sizes and film thickness. In addition, data will be presented to show how one of the underlying assumptions of perovskite manufacture, ambient processing, needs to be addressed to assure high quality perovskite solar cells are manufacturable. The ambient processing condition results might provide insight into why so many researchers have a high range of reported values for perovskite solar cells made in labs across the globe. The role of interface stability on the hole transport layer will also be investigated as the degradation of the PEDOT:PSS hole transport layer has a marked impact on the ability of the perovskites to have the long term performance demanded by solar farms. Finally, some of the first films of perovskites deposited via slot die onto flexible substrates are initially reviewed as the use of slot die and flexible substrates are considered the next steps in commercialization of the hybrid perovskite solar cell system.