Hole transporting materials (HTMs) for perovskite solar cells (PSCs) are limited in their use by processability, work function, and cost. Here we present a family of HTM polymers, synthesized via the Buchwald-Hartwig cross coupling reaction, utilizing low cost monomers with high yields. Removal of palladium and control of polydispersity are achieved through simple precipitations, vastly reducing the time and cost of workup. Through careful choice of functional groups, both pendant and in the backbone of the polymer, we demonstrate the ability to tune the highest occupied molecular orbital (HOMO) energies of these materials between -4.87 eV and -5.36 eV, allowing for use with perovskite active layers with narrow and wide bandgaps. Functional group choice also dictates the hydrophobicity of these materials, as well as ink affinity, with these two trends being significantly different. This family of polymers also achieved excellent conductivities, ranging from 0.2 mS/cm for polymers with electron withdrawing groups in the pendant moiety to 3.37 mS/cm for polymers with electron donating groups in that position, with PTAA measured at 0.54 mS/cm. When incorporated into devices with the FAMACs triple cation perovskite, the top performing materials demonstrate excellent PCE (18.79%) relative to state-of-the-art PTAA (17.93%), with superior performance over 1000 hrs under constant load. We demonstrate improvement of devices with HTM polymers with lower polydispersity and higher Mn, due to slight improvements in open circuit voltage, short circuit current and fill factor.

Low-cost, high efficiency polymer hole transport materials for perovskite solar cells

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ACS Fall 2022

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