Star-Shaped Organic Semiconductor with Extraordinary Thermomechanical Property and Solution Processability for Stable Perovskite Solar Cells

Achieving the desired thermomechanical properties for highly solution-processable organic semiconductors is challenging but crucial for heat tolerance of emerging optoelectronic devices. To this end, the successful synthesis of triphenylene–ethylenedioxythiophene-dimethoxytriphenylamine (TP–ETPA), a star-shaped organic semiconductor, is reported through a direct arylation reaction that involves ETPA, an electron donor, being grafted densely onto TP, which possesses six electron-equivalent functionalization sites. Remarkably, TP–ETPA exhibits significantly improved hole mobility compared to 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene (spiro-OMeTAD) at a given hole density, owing to its lower energetic disorder, larger average centroid distance, and smaller reorganization energy. TP–ETPA, with a molecular weight of 2888 Da and lacking flexible chains, demonstrates extraordinary solubility in nonpolar solvents, enabling the formation of dense, pinhole-free films through solution codeposition with an air-doping promoter. By utilizing the p-doped TP–ETPA composite as the hole transport layer, perovskite solar cells with an average power conversion efficiency of 23.4% are successfully fabricated. Notably, these devices display significantly enhanced operational stability and thermal stability at 85 °C. Molecular dynamics simulations reveal that the TP–ETPA-based hole transport layer possesses a high cohesive energy density, resulting in a large elastic modulus and slow diffusion of external species.