Perylene-Based Conjugated Polymers for Efficient and Stable Perovskite Solar Cells: The Superior Role of the Alkyl Side Chain over Oligo(ethylene glycol)

We synthesized two high HOMO energy level hole-transporting conjugated polymers, p-NP-E-BOC6-E and p-NP-E-BO2EG-E, through direct arylation polymerization. Copolymerization of 3,10-dibromo-1-(2-octyldodecyl)-1H-phenanthro[1,10,9,8-cdefg]carbazole with either 5,5′-(2,5-bis(hexyloxy)-1,4-phenylene)bis(3,4-ethylenedioxythiophene) or 5,5′-(2,5-bis(2-(2-methoxyethoxy)ethoxy)-1,4-phenylene)bis(3,4-ethylenedioxythiophene) yields the desired polymers. The presence of the (2-methoxyethoxy)ethoxy side chain, offering enhanced flexibility, results in higher hole mobility at the same hole density, probably due to a reduced π–π stacking distance within the conjugated backbone. Hexyloxy, exhibiting a stronger electron-donating ability than 2-methoxyethoxy–ethoxy, leads to higher hole density and enhanced conductivity under identical processing conditions. Moreover, both polymers display hole density-dependent mobility and conductivity. Notably, p-NP-E-BOC6-E exhibits a higher glass transition temperature and lower diffusion coefficient for external species, including 4-tert-butylpyridinium, bis(trifluoromethanesulfonyl)imide, HI, and H2O. When employed as the p-doped hole transport layer in perovskite solar cells, p-NP-E-BOC6-E achieves an average efficiency of 21.6%, while p-NP-E-BO2EG-E reaches 20.4%. Remarkably, p-NP-E-BOC6-E demonstrates improved long-term operational stability and storage stability at 85 °C compared to p-NP-E-BO2EG-E. These findings emphasize the superior role of alkyl groups over oligo(ethylene glycol) in designing hole-transporting conjugated polymers for perovskite solar cells.