Disentangling perovskite surface work functions and electron extraction energy offsets to drive high photovoltaic efficiency

Reducing nonradiative recombination is a main challenge in manufacturing highly efficient optoelectronic devices. Perovskite solar cells (PSCs) typically feature significant nonradiative recombination originating from energetic mismatch at the charge-extracting contact. Here, we widely manipulate the energy offset between the perovskite conduction band minimum (CBM) and the electron transporting state of the fullerene cathode interface layer in p-i-n PSCs by modifying the perovskite surface work function with defect-passivating self-assembled monolayers (SAMs) inducing surface dipoles. It is found that reducing the energy offset for electron extraction at such perovskite/fullerene electron-selective heterointerface from 0.98 to −0.02 eV yields a clear linear improvement in PSC built-in potential, with fill factor, photovoltage and power conversion efficiency all increasing as well. We further demonstrate that the improved photovoltaic performance is attributed to reduced energy offsets between the perovskite CBM and the fullerene electron accepting state, which accelerates electron extraction from perovskite and thus effectively suppresses nonradiative recombination. Moreover, the models of corresponding energy level alignment are proposed to discuss the impacts on PSC performance. Our work highlights the importance of tuning the work function even for defect-passivated perovskite surfaces to achieve barrier-less charge extraction and thus boost PSC performance.