Cu-Based Metal–Organic Frameworks for Photovoltaic Application

Abstract

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.

Enhanced photovoltaic performance of Cu-based metal-organic frameworks sensitized solar cell by addition of carbon nanotubes

“…These results show that MOFs are photoactive but it cannot conduct electricity. In addition to the previously reported findings27, this result also supports that iodine improves the conductivity of the MOFs dramatically. Fig.…”

“…As compared to the TiO 2 -MWCNTs composite film, the XRD patterns of the film after MOF sensitization are quite different. After sensitization, the film exhibited many additional new XRD signals at around 2 theta = 5° ~ 20°, which are the characteristic peaks of MOFs27. This result confirms the deposition of Cu-MOFs into the TiO 2 -MWCNTs composite film.…”

“…This finding reveals the deposition of Cu-MOFs into the composite film. As demonstrated previously27, conductivity of the Cu-MOFs is close to an insulator and iodine doping is required to modify the conductivity. Therefore, iodine doping into the frameworks of the composite film was carried out in order to improve the conductivity and the charge transfer across TiO 2 /MOFs interfaces.…”

“…In addition, as in the case of dye sensitized solar cells35, the photogenerated electrons from the LUMO level of the MOFs are needed to be transferred into the conduction band of TiO 2 (if the sensitizer is used to sensitize TiO 2 ). Previously, it has been shown that the energy levels of TiO 2 and the Cu-MOFs are well matching for the MOFs to be used as sensitizer of TiO 2 27. The ability of the MOF sensitizer to transfer photoelectrons from its LUMO level to the conduction band of TiO 2 and the influence of MWCNTs on this electron transfer process is investigated by measuring PL emission.…”

Facile interfacial charge transfer across hole doped cobalt-based MOFs/TiO2 nano-hybrids making MOFs light harvesting active layers in solar cells

“…However, appropriate assembly of MOFs into TiO 2 films can drastically affect the electron transportation behaviour and this is crucial for their applications. Based on our previous experience [37][38][39] , and on the basis of hit-and-trial on photocurrent-voltage (J-V) curve measurements, 20 LBL sensitization cycles of MOFs were optimized. Fig.…”