Simple Approach to the Highly Efficient and Cost-Effective Inverted Perovskite Solar Cells via Solvent-Engineered Electron-Transporting Layers of Fullerene

With dramatic growth in the photovoltaic (PV) market, perovskite solar cells (PSCs) have achieved remarkable performance and demonstrated enormous potential for use in next-generation PVs. In particular, inverted PSCs have advantages in lowering manufacturing costs because they are suitable for low-temperature printable processability and compatibility with existing silicon PVs for tandem cells. However, for the successful commercialization of PSC-based modules, material cost, a crucial factor, has not been considered in depth. Most inverted PSCs with the highest performance usually consist of fullerene derivatives, which are expensive but difficult to replace with other materials. Therefore, a rational method is needed to solve this problem, and we propose a simple idea to reduce material costs. We systematically investigated the correlation between the properties of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) films and various solvents with different boiling points. We discovered that the highly volatile dichloromethane (DCM) solvent forms a thick and uniform PCBM layer even at quarter concentrations. The DCM–PCBM layer improves the interfacial properties of the PCBM–perovskite film, leading to a device with superior performance compared to that of a device prepared with the PCBM layers from the other solvents. Finally, we successfully demonstrated a high-efficiency inverted PSC based on DCM–PCBM with a maximum power conversion efficiency (PCE) of 22.4%.