Understanding\nthe Impact of SAM Fermi Levels on High\nEfficiency p‑i‑n Perovskite Solar Cells

Completing the picture of the underlying physics of perovskite\nsolar cell interfaces that incorporate self-assembled molecular layers\n(SAMs) will accelerate further progress in p-i-n devices. In this\nwork, we modified the Fermi level of a nickel oxide–perovskite\ninterface by utilizing SAM layers with a range of dipole strengths\nto establish the link between the resulting shift of the built-in\npotential of the solar cell and the device parameters. To achieve\nthis, we fabricated a series of high-efficiency perovskite solar cells\nwith no hysteresis and characterized them through stabilize and pulse\n(SaP), JV curve, and time-resolved photoluminescence (TRPL) measurements.\nOur results unambiguously show that the potential drop across the\nperovskite layer (in the range of 0.6–1 V) exceeds the work\nfunction difference at the device’s electrodes. These extracted\npotential drop values directly correlate to work function differences\nin the adjacent transport layers, thus demonstrating that their Fermi\nlevel difference entirely drives the built-in potential in this device\nconfiguration. Additionally, we find that selecting a SAM with a deep\nHOMO level can result in charge accumulation at the interface, leading\nto reduced current flow. Our findings provide insights into the device\nphysics of p-i-n perovskite solar cells, highlighting the importance\nof interfacial energetics on device performance.