Surface Passivation Strategies of Perovskite Solar Cells

Perovskite solar cells (PSCs) have shown a remarkable improvement in efficiency over the past few years, giving high hopes for the future application of this technology in solar photovoltaic electricity production at industrial scale. Nowadays PSCs are inferior to crystalline silicon, especially in terms of efficiency and stability, thus preventing large scale market entry. A common issue of these cells involves the contact surfaces between the perovskite absorber and the charge extraction layers. High densities of superficial defects cause significant non-radiative recombination of charge carriers, thus lowering the achievable open circuit voltage. The work's focus is the interface between the perovskite and the electron transport layer of p-i-n PSCs, modified by introducing low-dimensional perovskites through novel passivation techniques. The analysis deals primarily with a triple cation perovskite composition, optimized for use as top subcell in perovskite/\CuInSe2 tandem solar cells (TSCs). Promising approaches have been compared to select the highest-performing processes before application in tandem devices. Inspired by multiple research papers, the newly developed passivation treatments are based on solutions of phenethylammonium (PEA) salts and perovskite precursors in organic solvents. Upon selection of the most suitable halide ion composing the large cation salt, optimizations of solution concentration and molar ratios were realized. A combination of PEA chloride and methylammonium iodide produced the greatest, although incremental, improvement in power conversion efficiency. To characterize the fabricated devices, photoluminescence quantum yield, x-ray diffraction, and charge extraction analyses were carried out, giving insights into how the investigated solutions modify the perovskite interface.