Wide-Bandgap Perovskite Solar Cell Using a Fluoride-Assisted Surface Gradient Passivation Strategy

Wide-band gap (1.68 eV) perovskite solar cells (PSCs) are important components of perovskite/Si tandem devices. However, the efficiency of wide band gap PSCs has been limited by their huge open-circuit voltage (V_oc ) deficit due to non-radiative recombination. Deep-level acceptor defects are identified as the major killers of V_oc , and they can be effectively improved by passivation with ammonium salts. Theoretical calculation predicts that increasing the distance between F and -NH₃ ⁺ of fluorinated ammonium can dramatically enhance the electropositivity of -NH₃ ⁺ terminals, thus providing strong adsorption onto the negatively charged I_A and I_Pb anti-site defects. Characterizations further confirm that surface gradient passivation employing p-FPEAI demonstrates the most efficient passivation effect. Consequently, a record-efficiency of 21.63 % with the smallest V_oc deficit of 441 mV is achieved for 1.68 eV-band gap inverted PSCs. Additionally, a flexible PSC and 1 cm² opaque device also deliver the highest PCEs of 21.02 % and 19.31 %, respectively.