Study On Interface Characteristics for Stable and Efficient Perovskite Solar Cells

Abstract

Perovskite solar cells have gained attention due to their high power conversion efficiencies. Despite these recent achievements of perovskite solar cells, their instability in air limit their potential for commercialization. In this dissertation, a study on the interface of the perovskite solar cells was carried out with the aim of improving their stability as well as efficiency, for practical application in air. Firstly, the role chemical degradation plays in moisture‐affected devices was investigated, and, based on this concept, a technique that enhances the device stability of p‐i‐n PSCs was developed. By surface treatment of the [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) layer with hydrophobic stearic acid and ethylenediamine, increased moisture resistivity of PCBM was achieved. The treated surface of the PCBM layer had improved hydrophobicity, with a contact angle of 108°, and also prevented water ingress in the perovskite layer longer than non‐treated surfaces. In addition, interfacial stability was enhanced by the suppressed interaction between the ions and the electrodes, resulting in treated devices exhibiting improved stability in their photovoltaic parameters compared to non‐treated devices when exposed to a dark environment with a relative humidity of 45%. Secondly, interface modification was used to facilitate the fabrication of perovskite films in air. This was carried out by introducing 2-dimensional perovskite at the base of a 3-dimensional active layer via coating of ethylenediamine bications on top of the hole transport layer of p-i-n planar configured devices. The cations induced thin 2-dimensional (2D) perovskite growth at the base of 3-dimensional (3D) perovskite to create 2D/3D hybrid active layer. This 2D layer in turn acted as a template for the growth of relatively large grains, 2 μm in diameter, compared to the micrometer-sized grains of pure 3D films. This stemmed from the fusion or merging of grain boundaries. The hydrophobicity of the 2D/3D film consequently improved, as evidenced by a large contact angle of 93.1°, compared to 68.9° for the 3D film. Because there are fewer defects sourced from grain boundaries, the 2D/3D devices yielded a high power-conversion efficiency of 16.11%, compared to 14.18% from conventional 3D perovskite devices. When stored in moderately humid environment of 50% RH, the 2D/3D devices exhibited longer stabilities, with 60% percent of their power conversion efficiencies maintained for 72 hours, compared to a total loss in efficiency for 3D device in the same time frame.