Interface\nModification for Energy Level Alignment\nand Charge Extraction in CsPbI3 Perovskite Solar Cells

In perovskite solar\ncells (PSCs) energy level alignment and charge\nextraction at the interfaces are the essential factors directly affecting\nthe device performance. In this work, we present a modified interface\nbetween all-inorganic CsPbI3 perovskite and its hole-selective\ncontact (spiro-OMeTAD), realized by the dipole molecule trioctylphosphine\noxide (TOPO), to align the energy levels. On a passivated perovskite\nfilm, with n-octylammonium iodide (OAI), we created\nan upward surface band-bending at the interface by TOPO treatment.\nThis improved interface by the dipole molecule induces a better energy\nlevel alignment and enhances the charge extraction of holes from the\nperovskite layer to the hole transport material. Consequently, a Voc of 1.2 V and a high-power conversion efficiency\n(PCE) of over 19% were achieved for inorganic CsPbI3 perovskite\nsolar cells. Further, to demonstrate the effect of the TOPO dipole\nmolecule, we present a layer-by-layer charge extraction study by a\ntransient surface photovoltage (trSPV) technique accomplished by a\ncharge transport simulation.