Setting standards for next-generation solar power

Perovskite solar cells (PSCs) are an emerging technology that scientists hope will offer a cheaper, more easily-produced alternative to silicon-based panels. However, the cells, based on crystalline materials known as perovskites, have long been marred by poor stability and vulnerability to environmental factors. 

A Swiss team from École polytechnique fédérale de Lausanne (EPFL), led by Konrad Domanski and financially supported by KACST, systematically investigated how PSCs degrade under environmental stress, and how the solar cell research community can improve their studies on these novel devices. 

Scientists have historically measured the robustness of PSCs using different techniques. This methodological variation makes it difficult to compare results, prompting Domanski’s team to discern the most reliable conditions for determining how PSCs deteriorate over time. 

The team found that light, temperature, atmosphere and electric load all degrade the performance of PSCs over time. While not statistically significant, ultraviolet (UV)-light-producing xenon lamps degraded PSC efficiency faster than non-UV-producing LED lights. Also, PSCs cycled through periods of light and dark (akin to a day/night cycle), but significantly recovered during dark periods. 

Oxygen also exhibited a detrimental effect, but only in the presence of light, suggesting a combined mechanism of action. High temperatures drastically deteriorated PSCs, attacking a weakness of the whole cell assembly, rather than the perovskite itself. For this reason, the EPFL team suggest that batch heat testing of PSCs could be a good first step to selecting devices for further testing. 

Regarding optimal conditions for standardized PSC testing, the team found that a solar simulator, set to the intensity of a bright sunny day, best imitated the natural illumination a PSC would normally have to endure. The investigations also suggested that the cells’ efficiency should be measured under both room and elevated temperatures, and that they should be configured to output the maximum possible power. 

Since oxygen and high humidity levels rapidly degrade the performance of PSCs and it’s easy to shield devices against them, Domanski’s team recommend testing the devices under a controlled atmosphere — enabling easier comparison of results.

1. Domanski, K., Alharbi, E. A., Hagfeldt, A., Grätzel, M., Tress, W. Systematic investigation of the impact of operation conditions on the degradation behaviour of perovskite solar cells. Nature Energy 3, 61-67 (2018). | article