Hole-Transport Layer Molecular Weight and Doping Effects on Perovskite Solar Cell Efficiency and Mechanical Behavior.

The effect of tuning molecular weight ( Mn) in poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) to increase both mechanical properties of the film and electrical properties of perovskite solar cells is reported. Perovskite solar cell devices are fabricated to investigate the effect of Mn on power conversion efficiency. Moisture stability for various Mn is also studied in PTAA films exposed to mechanical loads in humid environments. Furthermore, cohesion and tensile tests are employed to determine the mechanical properties of PTAA, where higher Mn leads to more robust films. To elucidate the effect of Mn on the debonding kinetics, a viscoelastic fracture kinetic model is proposed as a function of Mn, and the debonding mechanism is found to be dependent on Mn. Finally, the effect of small-molecule-based dopants on the mechanical stability of PTAA is investigated.