Solar cells could be produced more cost-effectively thanks to a new study on the use of perovskite films in solar cell technology. With the finite supply of traditional, non-environmentally friendly energy sources running out, there is increased focus on renewable energy sources, including replacements for expensive silicon-based solar cells. However, this research has brought perovskite solar cells closer to mass production by solving the key problems of efficiency, lifespan and scalability.
The study, by a team from the Okinawa Institute of Science and Technology Graduate University and reported in Energy & Environmental Science [Juarez-Perez et al. Energy Environ. Sci. (2016) DOI: 10.1039/C6EE02016J], examined organo-metal halide perovskite films, which have a highly crystalline structure and can be formed from many different chemical combinations, as well as being deposited relatively cheaply. They then assessed if the films could cheaply capture solar energy efficiently, be straightforward to produce and able to withstand an external environment.
“These findings deepen our understanding about perovskite degradation mechanisms, which is expected to provide insight for future rational design and optimization of perovskite materials and devices that can prevent or slow down degradation, and thus achieve longer lifetime”Yabing Qi
The team has already examined perovskite films in terms of a post-annealing treatment, uncovering the decomposition products of a specific perovskite, and also a new way to produce perovskites that maintains solar efficiency when scaled up. The post-annealing improvement resulted in less problems associated with grain boundaries, which manifest as gaps between crystalline domains and can lead to unwanted charge recombination. As this often reduces efficiency, such grain boundary problems were key to ensuring high performance. The resulting fused grain boundaries reduced charge recombination and provided useful conversion efficiency, with the films showing excellent stability and reproducibility.
However, when continuously operated, many perovskite solar cells can degrade quickly in ambient conditions, and in only a few days lose their photovoltaic properties. To avoid this effect, it was important to determine the major gas products of perovskite thermal degradation. Here, first author Emilio Juarez-Perez used thermal gravimetric differential thermal analysis and mass spectrometry to assess the mass loss and chemical nature of these products, demonstrating that the key gas products of degradation are methyliodide (CH3I) and ammonia (NH3). Knowing this helps to identify ways to prevent degradation, hopefully bringing more stable materials in the future.
As team leader, Yabing Qi, told Materials Today, “These findings deepen our understanding about perovskite degradation mechanisms, which is expected to provide insight for future rational design and optimization of perovskite materials and devices that can prevent or slow down degradation and thus achieve longer lifetime”. The researchers now plan to utilize their approach further to explore such new perovskite materials, and hopefully identify promising material candidates for high-efficiency, high-stability, low-cost solar cells.