In the last few years much research has gone into exploring the potential of perovskites as a material for solar cells, and improvements in their power conversion efficiency have certainly risen. Although lead halide perovskites have proven a recent success in photovoltaic applications, the toxicity of lead in such materials has been problematic. Now, however, high-quality lead-free, and therefore environmentally friendly, films based on double perovskites that offer useful photovoltaic properties have been developed in collaboration between Linköping University in Sweden and Nanyang Technological University in Singapore.
As reported in Advanced Materials [Ning et al. Adv. Mater. (2018) DOI: 10.1002/adma.201706246], the combined team have manufactured extremely high-quality single-layer thin films of densely packed crystals of double perovskites that can be used as the active layer in solar cells where sunlight is absorbed and charge carriers created. Charge carriers have demonstrated long electron-hole diffusion lengths in the material, a requisite for its suitability in the fabrication of planar structure double perovskite solar cells, in a breakthrough that could have important implications for the use of double perovskites in other optoelectronic devices such as lasers and light emitting diodes.
“We have taken the first major step and developed a method to manufacture the active layer. We have several good ideas of how to proceed to increase the efficiency in the near future.”Feng Gao
The applications for double perovskites as optelectronic materials are numerous, as they offer a large amount of potential candidates. In fact, there could be more than 4,000 different combinations of materials that can form double perovskites, and the team will attempt to calculate the combinations most appropriate for use in solar cells. The perovskites can be processed in a straightforward way from solutions with low-cost raw materials, offering promise for replacing silicon-based solar cells.
As it is difficult to prepare double perovskite films from precursors, the team prepared double perovskite single crystals, before preparing high-quality films from the crystals. However, the power conversion efficiency of the devices remains low, at just over 1% of the solar energy being converted to electricity, primarily due to the wide bandgap of this double perovskite. They hope to work to improve the light absorption properties through materials engineering, and also to optimize the absorption properties by forming alloyed double perovskites.
As researcher Feng Gao said, “we have taken the first major step and developed a method to manufacture the active layer. We have several good ideas of how to proceed to increase the efficiency in the near future.” Their next step is to tune the color of the double perovskites into dark so that they can absorb more light for efficient solar cells.