Functional additives for high-performance inverted planar perovskite solar cells with exceeding 20% efficiency: Selective complexation of organic cations in precursors

Imperfection originating from the ionic nature of organic inorganic hybrid perovskite (OIHP) is a major factor that degrades perovskite solar cells (PSCs) performance, and mitigating or removing it is essential for the implementation of high-performance PSCs. In this work, 2-hydroxyethyl acrylate (HEA), having both effective C[dbnd]O and O–H functional groups, is introduced as a functional additive that suppress imperfections by to control the crystallization process and passivate them at the same time, and the role of each function groups have been systematically investigated. We have found that O–H functional groups of HEA strongly interacts with organic cations (i.e., MABr, FAI) to form more stable organic cation-HEA complex selectively, delaying the crystallization process of perovskite. As a result, HEA improves crystallinity and grain size of perovskite and reduces charge trapping density by passivation and/or suppression of defect states. HEA raises average cell-efficiency from 17.37% to 19.01% and the maximum efficiency is reached to 21.01% for the inverted planar PSC. In addition, large-area (1.08 cm²) PSCs show an excellent efficiency of 20.40%, which is the highest efficiency in large-area inverted planar PSCs to date. PSCs with HEA also show long-term stability and better moisture resistance capabilities in ambient air conditions.