Inverted organic solar cells with solvothermal synthesized vanadium-doped TiO₂ thin films as efficient electron transport layer

We investigated the effects of using different thicknesses of pure and vanadium-doped thin films of TiO₂ as the electron transport layer in the inverted configuration of organic photovoltaic cells based on poly (3-hexylthiophene) P3HT: 6-6 phenyl-(6) butyric acid methyl ester (PCBM). 1% vanadium-doped TiO₂ nanoparticles were synthesized via the solvothermal method. Crystalline structure, morphology, and optical properties of pure and vanadium-doped TiO₂ thin films were studied by different techniques such as x-ray diffraction, scanning electron microscopy, transmittance electron microscopy, and UV-visible transmission spectrum. The doctor blade method which is compatible with roll-2-roll printing was used for deposition of pure and vanadium-doped TiO₂ thin films with thicknesses of 30 nm and 60 nm. The final results revealed that the best thickness of TiO₂ thin films for our fabricated cells was 30 nm. The cell with vanadium-doped TiO₂ thin film showed slightly higher power conversion efficiency and great J_sc of 10.7 mA/cm² compared with its pure counterpart. In the cells using 60 nm pure and vanadium-doped TiO₂ layers, the cell using the doped layer showed much higher efficiency. It is remarkable that the external quantum efficiency of vanadium-doped TiO₂ thin film was better in all wavelengths.