A team of researchers from École polytechnique fédérale de Lausanne (EPFL), Switzerland, have developed a method that improves both power conversion efficiency and stability of solar cells based on pure iodide as well as mixed-halide perovskites.

The new approach resulted in power-conversion efficiencies of 24.9% and 21.2% for two perovskite compositions. The team claimed about 90% and 80% of the initial efficiencies were retained after 1,200 and 250 hours of continuous operation, respectively.

“By addressing the critical issue of stability, our results represent an important step towards large-scale practical applications of PSCs,” the researchers said.

The research was carried out by Michael Grätzel and Ursula Rothlisberger at EPFL and led by Essa A. Alharbi and Lukas Pfeifer.

The Problem of Halide Segregation

A major obstacle in commercializing perovskite solar cells is their operational stability, which puts them at a disadvantage. Finding solutions to address this becomes crucial to make perovskite technology a success, especially for solar cells.

The problem outstands with mixed-halide perovskites, which are ideal materials for both tandem solar cells and emission-tunable LEDs because they combine high compositional flexibility with optoelectronic performance.

Mixed-halide perovskites also feature wide bandgaps, an essential property that affects the energy needed for a photovoltaic material to generate electricity.

However, in most mixed-halide perovskites, light can cause a “halide phase segregation,” wherein the ingredients tend to “de-mix” into regions of differing halide content. This segregation inevitably can lead to efficiency problems during the operational lifespan of a solar cell.

Addressing Challenges

The researchers said they used a method to treat perovskite solar cells with two alkylammonium halide modulators that work in synergy to improve solar cell performance.

The modulators are used as passivators — compounds used to mitigate defects in perovskites —  which otherwise promote degradation pathways.

In their study, the researchers were able to use the two modulators to stop halide segregation and substantially reduce the drops in power-conversion efficiency seen in the long-term use of perovskite solar cells.

Recently, researchers from Monash University, Australia, in collaboration with the Wuhan University of Technology in China, said they could use lead acetate as a precursor in making formamidinium-caesium perovskite solar cells with a conversion efficiency of 21%.

Earlier in the month, researchers from the Indian Institute of Technology (IIT), Roorkee, said they had successfully developed a prototype of a low-cost, high-quality perovskite solar cell that achieved a stable power conversion efficiency (PCE) of 17.05%.