Poly(3,/polystyrene sulfonate (PE-DOT:PSS) plays an important role in inverted planar perovskite solar cells (IPPSCs) as an efficient hole extraction and transfer layer (HTL). The IPPSCs based on PEDOT:PSS normally display inferior performance with a reduced open-circuit voltage. To address this problem, here sodium citrate-doped PEDOT:PSS is adopted as an effective HTL for improving the performance of IPPSCs. Sodium citrate-doped PEDOT:PSS HTL improves the conversion efficiency of IPPSCs from 15.05% of reference cells to 18.39%. The large increase of the open-circuit voltage (V OC ) from 1.057 to 1.134 V is the main source for this performance enhancement. With the help of characterization analysis of ultraviolet photoelectron spectroscopy, scanning electron microscopy, electrochemical impedance spectroscopy, etc., the higher work function of the doped PEDOT:PSS film and the uniform crystallinity of the perovskite film on it are disclosed as the reasons for the increased V OC and the consequent performance enhancement.

Cesium carbonate (Cs 2 CO 3 ) is a widely used interfacial modification material in organic solar cells (OSCs), organic light-emitting diode (OLED) and so on, which can: 1) lower the work function of metal electrode; 2) induce n-doping effect; and 3) alter the energy level of semiconductor materials under the action of dipole. Cs 2 CO 3 is selected in this study to modify the interface of perovskite solar cells (PSCs) and therefore improves the device performance. Further studies indicate that this performance improvement is due to the diffusion of Cs 2 CO 3 through [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) to form dipoles with perovskite to bend its energy level, resulting in an increased electron collection efficiency. This proposed mechanism for the interfacial modification of PSCs by bending the perovskite energy level through interfacial dipoles deepens the understanding of the role of interfacial layer.Due to their excellent photovoltaic properties such as direct bandgap, long carrier diffusion length, high optical absorption coefficient, high defect tolerance, suitable bandgap, and so on [1][2][3][4]

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