Figure. Copyright: NIMS
The ad hoc Team on Perovskite PV Cells (Team Leader: Kenjiro Miyano) of the Global Research Center for Environment and Energy based on Nanomaterials Science (GREEN) at the National Institute for Materials Science (NIMS) succeeded in producing highly reproducible and highly stable perovskite solar cells by using a low-temperature solution process, which is essential for realizing next-generation solar cells with such characteristics as low-cost, lightweight and flexible (Figure).
Conventional perovskite solar cells produced by a low-temperature solution process had problems in terms of stability and reproducibility, and details of their operational mechanism were difficult to clarify. In this research, the team newly developed a chlorine-mediated interdiffusion method, in which chlorine is added in the process of forming perovskite crystals, and realized high-efficiency perovskite solar cells having the following excellent characteristics by using a low-temperature solution process.
(1). A process temperature of less than 140°C at the most (high compatibility with flexible substrates, etc.)
(2). Excellent stability exhibiting consistent output characteristics for a long period
(3). Excellent durability maintaining stable output characteristics even under continuous light exposure for about two hours
(4). Highly reliable output characteristics and reproducibility exhibiting consistent conversion efficiency irrespective of the voltage sweep direction, etc.
Use of a low-temperature solution process makes it possible to produce solar cells with lightweight and flexible substrates such as plastic. In addition, the realization of highly stable, durable, and reproducible devices based on this research result enables detailed analysis of the operation of the devices even under continuous light exposure. Therefore, elucidation of the operational mechanism, which had been difficult in the past, is expected to advance remarkably toward practical application of perovskite solar cells.
The results of this research were achieved at GREEN, established under the “Program for Development of Environmental Technology using Nanotechnology” entrusted by the Ministry of Education, Culture, Sports, Science and Technology. The results were published in the June 14, 2015, issue of Journal of Materials Chemistry A, a journal issued by the Royal Society of Chemistry, UK, and presented at the 10th GREEN Symposium on June 20, 2015, along with the latest results obtained.
[Image caption: Schematic of the perovskite solar cell developed in this research and a scanning electron microscope image of its cross-sectional view (left) and output characteristics (right)
Light is absorbed in the perovskite layer, and electrons and holes (charge carriers) generated by photoexcitation are transported— electrons to the electron transporting layer (PCBM) and holes to the hole transporting layer. Then, they are extracted from the electrode, generating electric power with the output characteristics as shown on the right.]
