Enhancement of open-circuit voltage on organic photovoltaic devices by Al-doped TiO2 modifying layer produced by sol–gel method

• Easy and cheap solution-process for AlTiO2 modification of FTO electrode for OPVs
• Electrical, structural and optical characterization of TiO2 layers with Al-dopant
• Improvement of Voc and Jsc of inverted OPVs with AlTiO2 modified electrode

Sol–gel method has shown several advantages for oxide synthesis, such as lower cost production, coating large areas, lower processing temperatures and ease insertion of doping materials. Therefore, it is attractive for production of intermediate and electrode modifying layers in organic optoelectronic devices. Herein, spin-coated aluminum-doped titanium dioxide (AlTiO2) thin films were produced by sol–gel method onto glass and fluorine-doped tin oxide (FTO) substrates, using different Al-dopant concentrations and post-done annealing temperatures. Electrical measurements were performed in order to investigate the improvement of the TiO2 resistivity. Additionally, structural, compositional, morphological, optical and electrical properties of the optimal AlTiO2 modifying layers onto FTO substrates were probed by different techniques, and compared with those obtained from the undoped thin films produced under similar conditions. Organic photovoltaic devices (OPVs) with the structure FTO/AlTiO2(30 nm)/C60(50 nm)/CuPc(50 nm)/Al with an Al concentration of 0.03 M in AlTiO2 layer were produced. The insertion of AlTiO2 thin films improved the short-circuit current density (Jsc) as well as the open circuit voltage (Voc) in comparison with non-modified electrode FTO based devices. This behavior is discussed in terms of induced interface phenomena as dipole formation induced by Al.