Improved operational stability of perovskite solar cells

Hybrid perovskite is a material made from a metal halide framework interspersed with organic cations. They have attracted a great deal of interest in the solar energy sector because of their light capture capabilities combined with their low production costs, making perovskite solar cells (PSCs) a leading candidate to replace solar cells. current silicon-based devices. Perovskites also show great potential in a wide range of applications including LEDs, lasers and photodetectors.

One of the obstacles on the way to commercialization perovskite solar cells is their operational stability, which puts them at a disadvantage compared to the photovoltaic technologies already on the market. This is especially a problem with mix-halide perovskites, is the ideal material for parallelism solar battery and emission-regulated LEDs because they combine high compositional flexibility with optoelectronic performance.

Halide-mixed perovskite also has wide bandgaps, a property that affects the energy required for photovoltaic materials to generate electricity. But in most perovskites containing mixed halides, light can cause a phenomenon called halide phase separation, where the components “demix” into regions of different halide content. This separation can lead to significant efficiency problems throughout the operating life of the solar cell. Therefore, solving it is very important for the success of perovskite technology, especially for solar battery in the so-called parallel configuration, where wideband, halogen-mixed perovskites are often used in combination with a second low-banded perovskite or a silicon cell.

A team of researchers at EPFL’s School of Basic Science has now developed a method that improves both, energy conversion efficiency and stability, of pure iodide-based solar cells as well as halide-mixed perovskite, while preventing later halide phase separation. The article was published in Jouleand the research was carried out by the team of Professors Michael Grätzel and Ursula Rothlisberger at EPFL and led by Dr. Essa A. Alharbi and Dr. Lukas Pfeifer.

This method treats the PSCs with two alkylammonium halide modulators operating simultaneously to improve the efficiency of the solar cells. Modulators were used as passivates, compounds used to minimize defects in perovskite that would otherwise promote the aforementioned degradation pathways.

In this study, the researchers were able to use two modulators to stop halide distinction and thus significantly reduce the drop in energy conversion efficiency seen in long-term PSC use.

The new method results in an energy conversion efficiency of 24.9% for one perovskite component (α-FAPbI₃) and 21.2% for the other (FA₆₅GHOST₃₅Pb(I₆₅Br₃₅)₃). Approximately 90% and 80% of the initial efficiency is retained after 1200 and 250 hours of continuous operation, respectively. The authors write, “By addressing the critical issue of stability, our results represent an important step towards large-scale practical applications of PSC.”