Efficient Energy Level Modulation via Electrophilic KBF4 for High-Performance Inverted Planar Perovskite Solar Cells with Superior Stability

As a difficult problem for state-of-the-art perovskite solar cells (PSCs), interfacial energy loss leads to undesirable photovoltaic performance of PSCs, especially the open-circuit voltage (VOC). Interfacial energy level modulation has been proven as an effective strategy to minimize the interfacial energy loss with boosted VOC. Herein, an efficient energy level modulation layer, potassium fluoroborate (KBF4), is applied onto the surface of a nickel oxide (NiOX) hole transport layer in planar inverted PSCs. The BF4– group has a strong electron binding energy and high electrophilicity, which affect the electronic structure of the NiOX surface significantly. Therefore, with the thin KBF4 band modulation layer, the work function (WF) of NiOX increases, and the energy difference between the Fermi level and valence band decreases. This brings about a reinforced build-in field in comparison with the control film without KBF4, leading to acceleration of hole extraction and suppression of charge recombination. Consequently, a maximum power conversion efficiency (PCE) of 19.84% with a large VOC of 1.13 V is achieved with superior stability. This work focuses on studying the energy level management of NiOX-based inverted perovskite solar cells and offering a feasible path to design well-matched energy levels in PSC systems.