Conjugated Small Molecule for Efficient Hole Transport in High-Performance p-i-n Type Perovskite Solar Cells

The pi-conjugated organic small molecule 4,4'-cyclohexylidenebis[N, N-bis(4-methylphenyl) benzenamine] (TAPC) has been explored as an efficient hole transport material to replace poly(3,4-ethylenedio-xythiophene): poly(styrenesulfonate) (PEDOT: PSS) in the preparation of p-i-n type CH3NH3PbI3 perovskite solar cells. Smooth, uniform, and hydrophobic TAPC hole transport layers can be facilely deposited through solution casting without the need for any dopants. The power conversion efficiency of perovskite solar cells shows very weak TAPC layer thickness dependence across the range from 5 to 90 nm. Thermal annealing enables improved hole conductivity and efficient charge transport through an increase in TAPC crystallinity. The perovskite photoactive layer cast onto thermally annealed TAPC displays large grains and low residual PbI2, leading to a high charge recombination resistance. After optimization, a stabilized power conversion efficiency of 18.80% is achieved with marginal hysteresis, much higher than the value of 12.90% achieved using PEDOT:PSS. The TAPC-based devices also demonstrate superior stability compared with the PEDOT:PSS-based devices when stored in ambient circumstances, with a relatively high humidity ranging from 50 to 85%.