Role of the post-annealing conditions on the conductivity of niobium doped titanium dioxide electrodes prepared by sol–gel and their function in organic solar cells

In this work, we report the fabrication of indium tin oxide free organic solar cells and demonstrate the ability of niobium doped titanium dioxide (TNO) layers produced by sol–gel as feasible alternative electrode. The conductivity of the TNO was tailored by changing the layer thickness and the post-annealing conditions. Later, the crystal structure was revealed by X-ray diffraction. The post-annealing treatments were performed in a rapid thermal processing furnace under different gas atmospheres, temperatures and times. The conductivity of the samples was measured using a four-point set-up and the transparency through a UV–VIS spectrophotometer. A good sheet resistance of 181 Ω/□ is achieved when the electrode was heated in an N₂/H₂ atmosphere mixture at 1000 °C for 10 min. TNO based organic solar cells were manufactured and their performance was evaluated by current-voltage measurements. A power conversion efficiency of 0.71% was attained.