Atomic layer deposition of metal oxide buffer layer enabling the fabrication of high performance large area perovskite solar cells

Perovskite solar cells have been widely recognized as the most promising new type of photovoltaic technology due to its rapid development of power conversion efficiency from 3.8% to over 26% in merely fifteen years. However, the high performances were achieved mainly on small area cells with active area lower than 0.1 cm². When enlarging the active area of perovskite solar cells, the efficiency fell dramatically. How to reduce the gap between performances of small area and large area cells gradually becomes a critical point in the path towards the commercialization of perovskite photovoltaic technology. Herein, a strategy to pre-grow a thin layer of TiO₂ on rough FTO substrate by atomic layer deposition method before spin-coating SnO₂ nanoparticles was developed. The FTO substrate could be covered completely by TiO₂ due to the intrinsic conformal film growth mode of atomic layer deposition, thus the direct contact between local protuberance of FTO and perovskite layer could be prevented and the current leakage phenomenon could be prevented. X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy and dark current measurement further proved this point. Thanks to the approach, the repeatability and consistency of the small area cell fabrication technology on the same substrate were ameliorated obviously. The improved electron transport process revealed by photoluminescence results and incident light management process revealed by external quantum efficiency results also brought better solar cell performances. More importantly, highly efficient 0.5 cm² large area perovskite solar cells were fabricated through optimization of TiO₂ thicknesses. When growing 200 cycles TiO₂ (~9 nm thickness) using atomic layer deposition technology, the champion large area perovskite solar cell possessed a power conversion efficiency as high as 24.8% (certified 24.65%). The device performances also showed excellent repeatability between different fabrication batches. The perovskite solar cell with atomic layer deposited TiO₂ as buffer layer could retain over 95% of its initial efficiency after storage for 1500 hours under nitrogen atmosphere. The technique proposed in this paper could be helpful for the fabrication of perovskite solar cell modules in the realistic photovoltaic market and could be potentially extended to the large area fabrication of other perovskite optoelectronic devices such as light emitting diode, laser and detector.