Research Direction toward Scalable, Stable, and High Efficiency Perovskite Solar Cells

Discovery of the 9.7% efficiency, 500 h stable solid-state perovskite solar cell (PSC) in 2012 triggered off a wave of perovskite photovoltaics. As a result, a certified power conversion efficiency (PCE) of 25.2% was recorded in 2019. Publications on PSCs have increased exponentially since 2012 and the total number of publications reached over 13 200 as of August 2019. PCE has improved by developing device structures from mesoscopic sensitization to planar p-i-n (or n-i-p) junction and by changing composition from MAPbI₃ to FAPbI₃-based mixed cations and/or mixed anion perovskites. Long-term stability has been significantly improved by interfacial engineering with hydrophobic materials or the 2D/3D concept. Although small area cells exhibit superb efficiency, scale-up technology is required toward commercialization. In this review, research direction toward large-area, stable, high efficiency PSCs is emphasized. For large-area perovskite coating, a precursor solution is equally important as coating methods. Precursor engineering and formulation of the precursor solution are described. For hysteresis-less, stable, and higher efficiency PSCs, interfacial engineering is one of the best ways as defects can be effectively passivated and thereby nonradiative recombination is efficiently reduced. Methodologies are introduced to minimize interfacial and grain boundary recombination.