2, Taiwan International Graduate Program (TIGP), Sustainable Chemical Science and Technology (SCST), Academia Sinica, Taipei, , Taiwan
3, Department of Applied Chemistry, National Chiao Tung University, Hsinchu, , Taiwan
Hybrid organic-inorganic halide perovskite solar cells attract enormous attentions due to their excellent photovoltaic properties which can compete with that of the crystalline silicon solar cells. However, there are some issues in perovskite solar cell that need to be fully understood and solved before its commercialization. These include the operation mechanism, device stability, environment impact, and so on. In this study, charge extraction characteristics at the perovskite/TiO2 interface is studied by interface engineering. So that self-assembled monolayer of phosphonic acids with different chain length (spacer group) and functional (tail) group were adsorbed on mp-TiO2 to modulate the surface property and interfacial energy barrier to investigate the effect of surface modification on charge extraction and transport from the perovskite to the mp-TiO2 layer and thus the electrode. Two series of SAM-forming molecules with alkyl or phenyl as the spacer and various polar group as terminal substituents were prepared to tune the energy alignment and tunnelling distance at the mp-TiO2 and perovskite interface. The work function of the SAM-modified mp-TiO2 varied from -3.80 eV to -4.87eV, with that of the pristine mp-TiO2 at -4.19 eV. A correlation of charge mobility, charge extraction and transport with respect to the energy alignment of mp-TiO2 was attempted based on the systematic study. The study serves as a guide to engineer ETL interfaces with simple SAMs to improve the charge extraction, series resistance, and carrier balance. In this study, a maximum PCE of ~16.09% with insignificant hysteresis was fabricated, which is 17% higher than the standard device.