Fluorinated Polythiophenes\nwith Alkylthiophene Side\nChains Boosting the Performance of Wide Bandgap Perovskite Solar Cells

Wide bandgap (WBG) perovskite solar cells (PSCs) provide\ntheir\nmerit of high voltage output but are faced with the overdeepened valence\nband and the notorious phase segregation. Herein, two alkylthiophene-substituted\npolythiophenes (PT4T-0F and PT4T-2F) are applied as the interfacial\nlayer for the WBG (1.72 eV) PSCs. Compared with PT4T-0F, PT4T-2F with\nfluoride (F) on thiophene units in a conjugated backbone exhibits\nmore planar configuration, higher hole mobility, and deeper highest\noccupied molecular orbital energy. By using PT4T-2F as an additive\nin antisolvent, crystal growth of FA<sub>0.83</sub>Cs<sub>0.17</sub>Pb(I<sub>0.7</sub>Br<sub>0.3</sub>)<sub>3</sub> is successfully mediated,\nresulting in high ratio (100) plane exposure of the WBG perovskites,\nand defect passivation is simultaneously realized. The optimized device\npresents a high open-circuit voltage of 1.23 V and a power conversion\nefficiency of 19.20%. The long-term stabilities under moisture and\nthermal conditions are both improved. This work offers an ideal interlayer\nmaterial for WBG PSC engineering and further provides a simple process\nto integrate simultaneous crystal mediation and interface optimization.