Perovskite solar cells are a promising technology for low-cost, high-efficiency solar energy generation, but they currently have relatively low operational stability compared to traditional silicon-based solar cells. Scientists have found a way to improve the operational stability of perovskite solar cells, a crucial step towards their commercialization.
Metal halide frameworks are interspersed with organic cations to form hybrid perovskites. Because of their high light-harvesting capacity combined with low manufacturing costs, perovskite solar cells (PSCs) have sparked a lot of interest in the field of solar energy, making them prime candidates for replacing current silicon-based devices. Perovskites have also shown great promise in a variety of applications such as LED lights, lasers, and photodetectors.
One of the challenges in commercializing perovskite solar cells is their operational stability, which puts them at a disadvantage when compared to existing photovoltaic technologies. This is especially problematic for mixed-halide perovskites, which combine high compositional flexibility with optoelectronic performance and are ideal materials for tandem solar cells and emission-tunable LEDs.
The researchers were able to use the two modulators in this study to stop halide segregation and thus significantly reduce the drops in power-conversion efficiency seen in long-term PSC use.
Mixed-halide perovskites also have wide bandgaps, which affect the amount of energy required for a photovoltaic material to generate electricity. However, light can cause “halide phase segregation” in most mixed-halide perovskites, where the ingredients “de-mix” into regions with different halide content.
During the operational lifetime of a solar cell, this segregation can cause significant efficiency issues. Solving it is thus critical for the success of perovskite technology, particularly in solar cells with a so-called tandem configuration, in which mixed-halide, wide bandgap perovskites are commonly used in conjunction with a second low bandgap perovskite or a silicon cell.
To improve the operational stability of perovskite solar cells, several strategies can be employed:
- Using more robust and stable charge transport layers: The use of charge transport layers made from more stable materials, such as inorganic materials, can help to improve the stability of the solar cells.
- Encapsulation: Protecting the perovskite solar cells with a protective encapsulant can help to improve their operational stability by reducing exposure to moisture and other environmental factors.
- Using more stable electrodes: Using electrodes made of more stable materials, such as gold or silver, can help to improve the stability of the solar cells.
Overall, a combination of these strategies may be used to improve the operational stability of perovskite solar cells.
A team of researchers at EPFL’s School of Basic Sciences has now developed a method that improves both, power conversion efficiency and stability, of solar cells based on pure iodide as well as mixed-halide perovskites, while also suppressing halide phase segregation in the latter. The research was carried out by the groups of Professors Michael Grätzel and Ursula Rothlisberger at EPFL and led by Dr. Essa A. Alharbi and Dr. Lukas Pfeifer.
The method treats PSCs with two alkylammonium halide modulators that work synergistically to improve solar cell performance. The modulators were used as passivators, compounds used to mitigate defects in perovskites, which are otherwise promoting the aforementioned degradation pathways.
The researchers were able to use the two modulators in this study to stop halide segregation and thus significantly reduce the drops in power-conversion efficiency seen in long-term PSC use.
Power-conversion efficiencies of 24.9% for one perovskite composition (-FAPbI3) and 21.2% for the other (FA65MA35Pb(I65Br35)3) were obtained using the new method. After 1200 and 250 hours of continuous operation, respectively, approximately 90% and 80% of the initial efficiencies were retained. “By addressing the critical issue of stability, our results represent an important step toward large-scale practical applications of PSCs,” the authors write.
