Fluorinated polymer additives in Spiro-OMeTAD to improve the efficiency and stability of perovskite solar cells

This study demonstrates the transformative impact of incorporating poly(vinylidene fluoride-co-trifluoroethylene) P(VDF-TRFE) as an additive in the hole transport layer (HTL) of 2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (Spiro-OMeTAD). The P(VDF-TRFE) additive forms resilient coordination bonds with 4-tert-butylpyridine (TBP) and lithium bis(trifluoromethanesulfonyl)imide additives, which mitigates TBP evaporation and improves Spiro-OMeTAD film quality. In addition, we observed improvements in solar cell current–voltage characteristics consistent with increased Spiro-OMeTAD conductivity and suppressed non-radiative recombination at the HTL/perovskite interface. P(VDF-TRFE)-integrated devices exhibit an increment in power conversion efficiency (PCE) up to 24.1 % (reverse scan) from a reference PCE of 21.4 %. Furthermore, the unencapsulated P(VDF-TRFE)-integrated devices demonstrate improved stability, retaining over 90 % PCE after 45 days in an ambient atmosphere in the dark and 94 % PCE after 1080 h of continuous light-soaking in a nitrogen environment. This work demonstrates how additive engineering, as exemplified by P(VDF-TRFE), can effectively address stability and performance challenges within Spiro-OMeTAD in perovskite solar cells.