Cu-based metal-organic frameworks for photovoltaic application

In the present study, a thin layer of Cu-based metal-organic frameworks (MOFs, copper(II) benzene-1,3,5-tricarboxylate) is fabricated using a layer-by-layer technique, and the layer is investigated as a light-absorbing layer in TiO₂-based solar cells. Iodine doping of the MOFs is performed to improve the conductivity and charge-transfer reaction across the TiO₂/MOF/electrolyte interface. The HOMO and LUMO energy states of the MOF films are estimated to be -5.37 and -3.82 eV (vs vacuum), respectively, which show a well-matched energy cascade with TiO₂. For the first time, a TiO₂-based solar cell is fabricated successfully using iodine-doped Cu-MOFs as an active layer, demonstrating a cell performance with J_sc = 1.25 mA cm^-2 and Eff = 0.26% under illumination of 1 sun radiation. In contrast, the cell with an undoped MOF layer exhibited J _sc = 0.05 mA cm^-2 and Eff = 0.008%. Electrochemical impedance spectroscopy of the cells suggests that iodine doping significantly reduces the charge-transfer resistance.