Letian Dou, an assistant professor in the Davidson School of Chemical Engineering, worked on the article, “Thermochromic halide perovskite solar cells,” which focuses on the team’s research of the structural-phase transition behaviors in mixed halide perovskite thin films.
The phase transitions result in solar cell films with two switchable characteristic states, each having distinct visible transparencies and photovoltaic device efficiencies. These films are expected to be useful in the development of smart photovoltaic windows.
An illustration displays the day to night changes and potential power output in solar cell film transitions. (Image: Jia Lin)
“This study, for the first time, demonstrates that inorganic halide perovskites semiconductors are suitable for this type of device because of their ‘soft’ and ‘dynamic’ lattice, which allow reversible phase transition without degrading the electronic properties,” Dou said. “This is fundamentally different from traditional semiconductors such as Si or GaAs. This discovery will now open up new applications for semi-transparent solar cells. We can now tune their color.”
In addition to Dou, the team includes researchers from the University of California-Berkeley’s departments of Chemistry and Materials Science and Engineering; the U.S. Department of Energy’s Lawrence Berkeley National Laboratory, Berkeley, Calif.; Shanghai University of Electric Power, Shanghai, China; Berzelii Center EXCELENT on Porous Materials, Stockholm University, Stockholm, Sweden; Lawrence Livermore National Laboratory, Livermore, Calif; and Kavli Energy NanoScience Institute, Berkeley, Calif.
In this work, Dou contributed to the design of the device architecture and the phase transition dynamics study.
Chemical Engineering Assistant Professor Letian Dou talks about his research in hybrid materials synthesis and processing for the next generation energy harvesting and optoelectronics devices.
The solar cells undergo reversible transitions, which are thermally driven at 150-200 degrees Celsius and moisture mediated. Researchers found the cells transition between a transparent, non-perovskite phase with 81.7 percent visible transparency and a low power output to a deeply colored perovskite phase with a reduced transparency of 35.4 percent and a high power output. The solar cell features high thermal stability and fully reversible color and performance, both of which are key requirements for successfully integrating the cells into diverse applications.
Smart photovoltaic windows represent a promising green technology, with practical integrated applications in buildings, automobiles, information displays and many other technologies. Current semi-transparent photocells are effective in providing light, shade, and power output, but these photocells do not have any color-changing characteristics. Smart photovoltaic windows, as researched by the team, provide all of the same aspects as semi-transparent photocells, and also allow switchable transparencies that harvest and manage incoming solar energy.
Dou notes that the all-inorganic phase transition system developed in his team’s research is more robust toward degradation.
“The films can be switched over 100 times without obvious degradation, making the inorganic perovskites more suitable for commercial applications,” he said. “The research team is now exploring new materials toward lower-phase transition temperatures and faster transition kinetics.”