This Faculty Early Career Development (CAREER) Program grant aims to break new ground in the manufacturing of high-efficiency thin-film solar cells through electrospray deposition. Presently, nearly all commercial thin-film solar cells involve costly vacuum environments and rare earth materials, which are in limited supply. To help reduce the manufacturing cost and ease the nation's dependence on rare earth elements, this award supports fundamental research on a solution-based solar cell manufacturing process that operates at atmosphere pressure and uses only earth-abundant materials such as perovskites. Perovskite solar cells have exhibited power conversion energies above 15 percent, which is higher than the best organic solar cells, and have the potential of approaching 30 percent. The knowledge generated will enable a scalable, roll-to-roll manufacturing process of flexible thin-film (<300 nm) solar cells. The process uses extremely fine spray generated by an electrostatic liquid atomization technique to coat a substrate with a thin and uniform layer of liquid film. The drying of the liquid film will be judicially controlled to enhance the quality of the solidified thin-film and boost the power conversion efficiency. This research project crosscuts multiple disciplines such as manufacturing, thermo-fluid science, and materials science. The broad appeal of solar energy renders an excellent educational opportunity to increase public scientific literacy, engage women and other underrepresented student groups in physical sciences, and better prepare students to contribute to a modern workforce.
Polycrystalline perovskite solar cells have rapidly emerged as strong contenders for efficient solar energy conversion devices because perovskite photovoltaic materials are earth abundant, inexpensive, and can be processed at moderate temperatures and atmospheric pressure. These relaxed processing conditions expand the selection of compatible substrates thereby enabling technologies such as tandem solar cells and roll-to-roll fabrication. However, two major challenges remain. First, the liquid films tend to rupture and de-wet during drying, leaving significant portion of substrate area uncovered. Second, scalable manufacturing processes for ultra-thin (<300 nm) perovskite films are still lacking. The proposed research undertakes the dual challenges of film rupture and manufacturing scalability. The idea of regulated drying of thin liquid films is proposed to suppress spontaneous rupture of the wet film, reduce detrimental pin-hole formation, improve crystal structure and, consequently, increase the power conversion efficiency. The research team will formulate a theoretical model to prescribe fluid mechanical and thermal boundaries that suppress film rupture. Model predictions will be compared and validated with experiments on regulated drying, followed by film characterization and device performance evaluation to reveal the interplay between processing, characteristics and performance.