A team of researchers, led by Professor Michael Grätzel at EPFL and Xiong Li at the Michael Grätzel Center for Mesoscopic Solar Cells in Wuhan (China), have developed a technique that addresses stability concerns of perovskite solar cells (PSCs) and increases their efficiency.
The researchers introduced a phosphonic acid-functionalized fullerene derivative into the charge-transporting layer of the PSC as a “grain boundary modulator”, which helps strengthen the perovskite crystal structure and increases the PSC’s resistance to environmental stressors like heat and moisture.
The team also developed a redox-active radical polymer called poly(oxoammonium salt) that effectively “p-dopes” the hole-transporting material – a crucial component of the PSCs. The polymer, acting as a "p-dopant," improves the conductivity and stability of the hole-transporting material, a crucial component of the cells. The process of “p-doping” involves introducing mobile charge electronic charge carriers into the material to improve its conductivity and stability, and in this case mitigated the diffusion of lithium ions, a major problem that contributes to the operational instability of PSCs.
With the new technique, the scientists achieved power conversion efficiencies of 23.5% for small PSCs and 21.4% for larger "minimodules." These efficiencies are comparable to traditional solar cells, with the added advantage of an improved stability for PSCs.
The solar cells retained 95.5% of their initial efficiency after more than 3200 hours of continuous exposure to simulated sunlight maintaining the temperature at 75 °C over the whole period, a significant improvement over previous PSC designs.
The new approach can revolutionize the use of PSCs, making them accessible for use on a larger scale. The researchers believe that their technique could be easily scaled up for industrial production and could potentially be used to create stable, high-efficiency PSC modules.