Main chain engineering of phenothiazine-based semiconducting copolymers for stable perovskite solar cells at 85 °C

Abstract

Semiconducting polymers hold significant promise for facilitating hole conduction in perovskite solar cells (PSCs). In this study, we employed a Pd-catalyzed direct arylation reaction to achieve high-yield synthesis of two alternating copolymers: p-PTZ-E and p-PTZ-EBEM, by reacting 3,7-dibromo-10-(2-octyldodecyl)phenothiazine with ethylenedioxythiophene (EDOT) and EDOT-dimethoxylphenylene-EDOT (EBEM), respectively. We examined the influence of the comonomers EDOT and EBEM on various properties of phenothiazine-based semiconducting polymers, including the energy level, glass transition temperature, water permeation, and hole transport. Notably, the amorphous films of both copolymers exhibited mobility and conductivity that depended on the hole density. We blended p-PTZ-EBEM with 4-tert-butylpyridinium bis(trifluoromethanesulfonyl)imide at a weight percentage of 7.5% to achieve a morphologically uniform film with an air-doped hole density of 1.0 × 10¹⁸ cm⁻³, a hole mobility of 1.4 × 10⁻³ cm² V⁻¹ s⁻¹, and an electrical conductivity of 225 μS cm⁻¹. Leveraging this air-doped p-PTZ-EBEM composite film as the hole transport layer, mesoporous titanium dioxide as the electron transport layer, and a ternary mixed-cation perovskite as the light absorption layer, we fabricated PSCs with power conversion efficiencies ranging from 21.0% to 21.8%. These cells exhibited remarkable operational stability and thermostability at 85 °C.