A comparative study of o,p-dimethoxyphenyl-based hole transport materials by altering π-linker units for highly efficient and stable perovskite solar cells

Abstract

Two easily synthesized o,p-dimethoxyphenyl-based hole transport materials (HTMs) containing biphenyl (HL-1) and carbazole (HL-2) in the π-system, respectively, have been designed and studied for perovskite solar cells (PSCs). A higher efficiency of 18.34% for the HL-2 based device was obtained compared to that of HL-1 showing a lower efficiency of 16.14%. A small hysteresis was also observed in the HL-2 based device while the HL-1 based device displayed a significant hysteresis. As a carbazole unit has a stronger electron-donating ability than biphenyl, HL-2 shows a higher hole mobility. The steady-state photoluminescence characteristics confirm that HL-2 can efficiently extract charge carrier at the perovskite/HTM interface rather than HL-1. Meanwhile, a compact HL-2 film without pin-holes effectively suppressed the non-radiative recombination at the interface, resulting in the improvement of the fill factor and open voltage. Most importantly, the steric hindrance due to the long hexyl chain of HL-2 could restrain the halogen migration from the perovskite to the Ag electrode. Thus, the HL-2 based device without encapsulation showed an advanced thermal stability at 85 °C after storing for 100 h compared to the HL-1. These results indicate that the o,p-dimethoxyphenyl unit is a promising alternative to develop small molecular HTMs for highly efficient and stable PSCs.