Optimization of a compact layer of TiO₂ via atomic-layer deposition for high-performance perovskite solar cells

We report the effect of thickness of a film consisting of a compact layer of TiO₂ produced via atomic-layer deposition (ALD) for mesoporous perovskite solar cells (PSCs) with a n-i-p configuration. Uniform and pinhole-free TiO₂ films of thickness from 10 to 400 nm were deposited on fluorine-doped tin-oxide substrates using ALD. The device performance of the PSC showed a trend systematic with the thickness of the ALD-TiO₂ compact layer and attained the best efficiency, 15.0%, of power conversion at thickness 200 nm. Photoluminescence (PL) spectra and the corresponding PL decays for perovskite (PSK) deposited on varied ALD-TiO₂ films were recorded; the effective PL quenching is due to electron transfer from PSK into the ALD-TiO₂ compact layer. The most efficient interfacial electron transfer occurred at film thickness 200 nm, for which the ALD-TiO₂ film has the greatest surface roughness and conductivity. We found a systematic correlation between the device performance in relation to the conductivity and the rate of interfacial electron transfer as a function of thickness of the ALD-TiO₂ film; the best performance occurred at thickness 200 nm. The devices showed great stability and reproducibility, providing an alternative for high-performance PSCs with a well-controlled TiO₂ compact layer.