(Invited) Development of Perovskite Photovoltaic Devices Using Electrodeposition

Abstract

Photovoltaic energy is considered today as the most useful natural energy source. To date, different types of solar technologies are industrially available, and the attempts in research and development to improve their potential are continuing. While a number of different materials with different efficiencies can achieve photovoltaic solar energy conversion, so far, no particular material or combination is cheap enough to compete with large-scale fossil fuel-generated electricity. Nowadays, Si-based cells are the most marketed, and they produce high solar conversion efficiencies. However, expensive high temperature and high vacuum processes are adopted in order to elaborate pure Si. Another active material, called perovskite, newly emerged in the solar community. It has attracted major attention worldwide because of its outstanding photovoltaic performance, easy fabrication process, adaptable band-gap, high extinction coefficient, and high carrier mobility. As perovskite is capable of generating a power conversion efficiency approaching that of the leading silicon and that the solar devices fabrication cost is lower, perovskite solar cells tend to be considered as the future of the photovoltaic technology.However, the most used method to deposit perovskite active layer is spin coating, which presents many constraints such as limited surface coverage, non-homogeneity, undefined perovskite crystallinity, and poor stability. Perovskite obtained by spin-coating requires working in inert environment (glove box) and adding some toxic additives to maintain the stability of the perovskite. This increases its cost and enables the deposition only on small surfaces. There is thus a need to look up for alternative deposition methods, more ecofriendly, at lower costs, applicable for large-scale production of perovskite solar cells.Electrodeposition recently started to be explored as an efficient alternative for perovskite fabrication. There have been several attempts over the past years to optimize the electrodeposited perovskite layer and adjust its crystallization on dissimilar layers. All sub-techniques started by electrodepositing an initial layer (PbO, PbO2 or PbI2) followed by one or several conversions of the as-deposited layer. In the presented work, we were able to develop different types of perovskites using electrodeposition, understand the impact of the different deposition parameters on their structure, and improve their stability comparing to the spin-coated ones. Along with the simple MAPbI3 perovskite, the electrodeposition of mixed MAPbI3-xClx and MA1-yFAyPbI3-xBrx perovskites will be presented. The present study is one of its kind, since these mixed perovskite were never developed using electrodeposition before. It was observed that using electrodeposition afford enhanced stability compared to spin-coating process, and the different fabricated perovskites were also proved to experience a positive maturation phenomenon during their first 500 hours of life.The electrodeposition process is easy to manipulate, and the electrodeposited films could grow on surfaces as large as desired, inside an electrolyte, allowing its application in ambient atmosphere, with no need of a glove box. It is also eco-friendly in terms of solvent engineering, since no toxic solvents are needed to stabilize or enhance the morphology of the obtained films. The main solvents used are deionized water, ethanol and isopropanol.