Structure and Process Engineering Facilitated by PAMAM Dendrimers for Highly Stable Perovskite Solar Cells

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Despite dramatic progress in efficiency, perovskite solar cells still must overcome some major problems before becoming economically competitive in the photovoltaic market. The main obstacles for commercialization of perovskite solar cells are short lifespan and long fabrication time. In this project, the short lifespan and manufacturing issues will be addressed through a novel process and device structure engineering enabled by a specific polymer material, polyamidoamine (PAMAM) dendrimers, while maintaining the efficiency. The proposed research will not only advance the knowledge in solar cell fabrication, but also impact society. The educational goal is to promote STEM education on advanced manufacturing of solar cells. Through this project, under-represented minority and female students will be hired to work on the proposed research, and research outcomes will be integrated in the teaching courses. As outreach activities, scientific modules on solar cells will be developed and demonstrated in the middle schools of the Black Belt region of Alabama, encouraging more minority students to enter STEM fields in their college study. Perovskite solar cells (PVSCs) suffer from instability, which leads to short lifetimes. The processing of these types of solar cells also requires long annealing times, and multiple deposition steps. In this project, device instability will be addressed from both active layer and charge transporting layers. With the incorporation of a specific polymer into the perovskite active layer, a condensed perovskite film will be attained, which will prevent penetration of moisture and oxygen, leading to significant improvement in stability. Device structure engineering will be based on the conventional inverted planar architecture with inorganic metal oxide as electron transporting layer and removal of hole transport layer. Because of the addition of PAMAM dendrimers, good adhesion and water resistance are ensured at the perovskite/ITO interface, precluding water diffusion into the perovskite absorber from the ITO side. The ITO work function will be increased through a chemical treatment, serving as an “invisible” hole transport layer to assist hole collection and block electron transport at the perovskite/ITO interface. Therefore, this structure engineering approach will not only enhance stability, but also maintain the promise of high power-conversion efficiency (PCE). To advance fundamental understanding on addition of PAMAM dendrimers, distribution of polymer additives in perovskite thin films will be characterized with Transmission Electron Microscopy (TEM), and in-situ characterization of defects, recombination, and carrier lifetime will be conducted for samples without polymer addition and with optimal polymer loading. In addition, an ultra-smooth ITO film will be attained through sputtering on polymer coated glass. The increase of rob-off resistance from the polymer on both sides of the ITO surfaces improves device reliability. Throughout this study, all the stacking layers of perovskite solar cells will go through rapid photonic annealing and sintering, paving the way for mass production of perovskite solar modules through low-cost, high-speed printing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.