Modified Fullerenes for Efficient Electron Transport Layer-Free Perovskite/Fullerene Blend-Based Solar Cells

A variety of novel chemically modified fullerenes, showing different electron-accepting capabilities, has been synthesized and used to prepare electron transport layer (ETL)-free solar cells based on perovskite/fullerene blends. In particular, isoxazolino[60] fullerenes are proven to be a good candidate for processing blend films with CH₃ NH₃ PbI₃ and obtaining enhanced power conversion efficiency (PCE) ETL-free perovskite solar cells (PSCs), improving the state-of-the-art PCE (i.e., 14.3 %) for this simplified device architecture. A beneficial effect for pyrazolino and methano[60]fullerene derivatives versus pristine [60]/fullerene is also shown. Furthermore, a clear correlation between the LUMO energy level of the fullerene component and the open circuit voltage of the solar cells is found. Apart from the new knowledge on innovative fullerene derivatives for PSCs, the universality and versatility of perovskite/fullerene blend films to obtain efficient ETL-free PSCs is demonstrated.