Researchers at Brazil's Federal University of ABC recently reported a way to mitigate the rapid degradation of perovskite solar cells when exposed to humidity and ambient temperature conditions during both manufacturing and use. This degradation affects the performance of the devices over time and therefore their durability.
The team describes a process that is unique in that it can be carried out without the strict humidity and temperature controls that exist in laboratories dedicated to researching these devices. The solar cells in the scientists' work were obtained under ambient conditions, without major humidity controls, which may be more compatible with industrial preparation conditions, according to Professor André Sarto Polo, coordinator of the study and member of the Center for Innovation on New Energies (CINE) – an Engineering Research Center (ERC) supported by FAPESP and Shell.
The perovskite family includes materials with different chemical compositions. They all share a common structure of positively charged ions (cations) and negatively charged ions (anions). Perovskites based on methylammonium (MA ) and formamidinium (FA ) cations are the most studied for use in solar cells.
In this study, the authors incorporated increasing amounts of formamidinium cations into methylammonium-based perovskites, characterized each of the materials obtained and assembled solar cells with them. The production and characterization of the materials and devices were carried out in environments with relative humidity ranging from 40% to 60%.
To test their stability, these solar cells were exposed to ambient temperature and humidity for 90 days. During this period, the researchers systematically studied the properties of all the devices in order to determine the influence of the addition of formamidinium on the performance of the solar cells.
While solar cells without FA showed a sharp drop in efficiency immediately after assembly and stopped working after 30 days, cells with more than 25% FA+ maintained 80% efficiency at the end of 90 days.
“This work demonstrates how the incorporation of FA cations into MA -based perovskites causes an increase in the durability of perovskite solar cells fabricated and measured under ambient conditions,” summarizes Polo.
According to him, this is because the addition of formamidinium causes an increase in the size of the grains that make up the crystalline structure of the perovskite, reducing the overall length of the edges. Since the edges are points where moisture accumulates, the perovskite suffers less degradation and the solar cell maintains its good performance for longer.
The research opens up the prospect of developing more durable perovskite solar cells that can be produced at lower cost and in more environmentally friendly conditions.