Optimized perovskite films claim record power conversion efficiencies
The international research team, which includes Uli Wiesner, the Spencer T. Olin Professor of Materials Science and Engineering, and Lara Estroff, associate professor of materials science and engineering, has demonstrated how to optimize the fabrication conditions of a thin film solar cell. The research results were published in Nature Communications.
The type of films the Cornell researchers made are organic-inorganic metal halide perovskites, which have been widely studied for solar applications.
The researchers arrived at near-perfect solar cells using a new liquid source, called a non-halide lead acetate. While perovskite solar cells have improved in a few short years, some basic properties of the light-absorbing material still were not well understood. Making the solar material starts with a solution of organic and inorganic molecules, and tuning the solution for smooth, defect-free perovskite films had not been perfected.
The researchers started with several kinds of liquid sources made of lead salts and studied the role that certain negatively charged ions – anions – played in the film formation. With the help of the Cornell High Energy Synchrotron Source, they characterized how the perovskites’ crystal structures varied depending on which lead salt solution was used. From there they could figure out which was optimal.
The method they settled on for growing the solar cells is also a simple solution-coating, which makes it attractive for commercial applications.
“By choosing the right precursor chemistry and via a simple one-step solution casting process, we obtained perovskite films with a smoothness surpassing that of vapor-deposited films, resulting in record power conversion efficiencies,” Wiesner said.
The research paper entitled ‘Ultrasmooth Organic-Inorganic Perovskite Thin-Film Formation and Crystallization for Efficient Planar Heterojunction Solar Cells’ includes work at four universities on three continents: Cornell, with Oxford University and Cambridge University in the United Kingdom, and Nanjing University in China.
It is the result of a longstanding collaboration between the Wiesner and Estroff labs at Cornell, and their interaction with Henry Snaith at Oxford University, a world leader in perovskite solar cell device fabrication.
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