Effects of Oxide Contact Layer on the Preparation and Properties of CH₃NH₃PbI₃ for Perovskite Solar Cell Application

Abstract

In perovskite solar cells, oxide electron transport layers (ETL) and their interface with the organometal trihalides are key to achieve efficient and stable devices. In the present work we investigate ZnO and TiO₂ ETLs and their influence on the preparation of CH₃NH₃PbI₃ film by two different techniques. In the “one-step” technique, a solution is used for the deposition of a precursor layer which is dripped and subsequently annealed. In the “two-step” sequential technique, a PbI₂ precursor layer is converted into perovskite. We show that, on ZnO, the annealing treatment of the “one-step” deposited layer is optimum for a duration time of only 2 min. This duration is much less critical for the TiO₂ underlayer. Long annealing times produce the degradation of the pigment and formation of PbI₂. It is also shown that the “one-step” technique gives better results for the sensitization of smooth oxide underlayers whereas the “two-step” one must be utilized for rough or structured underlayer sensitization. The best solar cell performances were achieved by combining a low-overvoltage electrodeposited ZnO layer, a planar architecture, and a perovskite layer prepared by a “one-step” deposition-dripping route. A maximum overall conversion efficiency of 15% was measured for the ZnO-based perovskite solar cell. Cell impedance spectra have been measured over a large applied voltage range. Their analysis, using an ad-hoc equivalent circuit, shows that charge recombinations are reduced for the “one-step” perovskite and that a better interface with the oxide is produced in that case