Bandgap tuning and compositional exchange for lead halide perovskite materials

Perovskite solar cells (PSCs) have rapidly emerged as a potential competitive photovoltaic technology reaching high power conversion efficiencies (PCEs) from single digits to a certified 23.7% in just a few years. At this stage, the key issues are the further improvement of the PCE and long-term device stability. In this chapter, we summarize the recent developments in the quest to phase stabilize the perovskite material. Since the organic cations are volatile and sensitive to moisture, heat, light and thus a long-term risk factor for phase stability, our focus is on incorporation of inorganic cations such as cesium and rubidium to enhance the photo-active black phases by means of modifications in optoelectronic properties of perovskites. The challenges associated with PSC industrialization include the role of cation/anion in phase stability, phase segregation of the halides, toxicity, organic/inorganic ion mixing and determination of the best tuned-band gap composition for tandem applications.