Balancing Energy-Level Difference for Efficient n-i-p Perovskite Solar Cells with Cu Electrode

Developing low cost and stable metal electrode is crucial for mass production of perovskite solar cells (PSCs). As an earth-abundant element, Cu becomes an alternative candidate to replace noble metal electrodes such as Au and Ag, due to its comparable physiochemical properties with simultaneously good stability and low cost. However, the undesirable band alignment associated with the device architecture impedes the exploration of efficient Cu-based n-i-p PSCs. Here, we demonstrated the ability of tuning the Fermi level (E_F) of hole transport layer (HTL) to reduce the energy level difference (Schottky barrier) between HTLs and Cu. Further, we identified that the balance of energy level difference between HTL and adjacent layers (including perovskite and Cu) is crucial to efficient carrier transportation and photovoltaic performance improvement in the PSCs. Under the optimized condition, we achieve a device power conversion efficiency (PCE) of 20.10%, which is the highest on the planar n-i-p PSCs with Cu electrode. Meanwhile, the Cu-based PSCs can maintain 92% of their initial efficiency after 1000 h storage, which is comparable with Au-based devices. The present work not only extends the understanding on the band alignment of neighboring semiconductor functional layer in the device architecture to improve the resulting performance but also suggests great potential of Cu electrode for application in PSCs community.