Reducing Interface Energy Loss of Perovskite Solar Cells by Molecular Engineering of Hole-Transporting Materials

Numerous novel hole-transporting materials (HTMs) have been reported in the literature, which play a vital role in enhancing the efficiency and stability of perovskite solar cells (PSCs). However, the PSCs using these HTMs continue to suffer from exciton recombination induced by energy level misalignment and defect states. Herein, an ingenious molecular design for HTMs (WD03 with triphenylethylene and WD04 with trithienylethylene) is reported to modulate their energy levels and passivation effectively. The optimal band alignment between WD03 and perovskite is crucial for enhancing the open-circuit voltage (V_oc), which minimizes the interface carrier recombination. The theoretical analysis reveals that replacing thiophene with benzene enhances the passivation ability of HTM, resulting in a more substantial passivation effect on the Pb-cluster defect of perovskite. These factors contribute to a high V_oc (1.194 V) of WD03-based cell, ranking among the highest values for n-i-p PSCs with a normal bandgap perovskite absorber. Moreover, the propeller-shaped WD03 strikes an excellent balance between charge transport and film quality. Owing to these advantages, the PSC based on dopant-free WD03 with surface modification attains a remarkable efficiency of 23.66% and the PSC based on doped WD03 reaches an exceptional efficiency of 25.79%. Following the substitution of trithienylethylene with triphenylethylene, the WD03-based cell exhibits enhanced stability compared to the cell based on WD04. This work emphasizes the significance of molecular engineering of HTMs in regulating energy level and passivation ability, which are crucial for achieving high V_oc and stability in PSCs.