Blading Phase‐Pure Formamidinium‐Alloyed Perovskites for High‐Efficiency Solar Cells with Low Photovoltage Deficit and Improved Stability

• Published in: Advanced materials (Weinheim) Vol. 32; no. 28; pp. e2000995 - n/a
• Main Authors: Wu, Wu‐Qiang, Rudd, Peter N., Wang, Qi, Yang, Zhibin, Huang, Jinsong
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.07.2020; Wiley
• Subjects: Alloying; charge collection; charge recombination; Circuits; Crystal defects; Crystal growth; Efficiency; Electric potential; Energy conversion efficiency; Energy gap; Grain boundaries; Illumination; Inks; light harvesting; Moisture; Optoelectronics; passivation; perovskite solar cells; Perovskites; Phase stability; Photoelectric effect; Photoelectric emission; Photovoltaic cells; Solar cells; SOLAR ENERGY; Surface stability; Voltage; charge collection; passivation; charge recombination; light harvesting; perovskite solar cells
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202000995

Currently, blade‐coated perovskite solar cells (PSCs) with high power conversion efficiencies (PCEs), that is, greater than 20%, normally employ methylammonium lead tri‐iodide with a sub‐optimal bandgap. Alloyed perovskites with formamidinium (FA) cation have narrower bandgap and thus enhance device photocurrent. However, FA‐alloyed perovskites show low phase stability and high moisture sensitivity. Here, it is reported that incorporating 0.83 molar percent organic halide salts (OHs) into perovskite inks enables phase‐pure, highly crystalline FA‐alloyed perovskites with extraordinary optoelectronic properties. The OH molecules modulate the crystal growth, enhance the phase stability, passivate ionic defects at the surface and/or grain boundaries, and enhance the moisture stability of the perovskite film. A high efficiency of 22.0% under 1 sun illumination for blade‐coated PSCs is demonstrated with an open‐circuit voltage of 1.18 V, corresponding to a very small voltage deficit of 0.33 V, and significantly improved operational stability with 96% of the initial efficiency retained under one sun illumination for 500 h. A multifunctional conjugated benzene ammonium halide is introduced to enhance phase purity, reduce trap‐state density, and suppress nonradiative charge recombination. Blade‐coated solar cells based on stabilized formamidinium‐dominant perovskite compositions deliver an impressive efficiency of 22.0% and an improved operational stability.