Ionic Liquid Treatment for Highest‐Efficiency Ambient Printed Stable All‐Inorganic CsPbI3 Perovskite Solar Cells

• Published in: Advanced materials (Weinheim) Vol. 34; no. 10; pp. e2106750 - n/a
• Main Authors: Du, Yachao, Tian, Qingwen, Chang, Xiaoming, Fang, Junjie, Gu, Xiaojing, He, Xilai, Ren, Xiaodong, Zhao, Kui, Liu, Shengzhong (Frank)
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.03.2022
• Subjects: ambient printed devices; Blade coating; Cesium; Crystal defects; crystal growth; Crystallization; CsPbI 3 perovskite solar cells; defects passivation; Energy conversion efficiency; Film growth; Grain boundaries; High temperature; Illumination; Interface stability; Interfacial energy; Ionic liquids; Ions; Lattice strain; Lattice vacancies; Perovskites; Phase stability; Photovoltaic cells; Solar cells; Thin films
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202106750

All‐inorganic cesium lead triiodide (CsPbI3) perovskite is well known for its unparalleled stability at high temperatures up to 500 °C and under oxidative chemical stresses. However, upscaling solar cells via ambient printing suffers from imperfect crystal quality and defects caused by uncontrollable crystallization. Here, the incorporation of a low concentration of novel ionic liquid is reported as being promising for managing defects in CsPbI3 films, interfacial energy alignment, and device stability of solar cells fabricated via ambient blade‐coating. Both theoretical simulations and experimental measurements reveal that the ionic liquid successfully regulates the perovskite thin‐film growth to decrease perovskite grain boundaries, strongly coordinates with the undercoordinated Pb2+ to passivate iodide vacancy defects, aligns the interface to decrease the energy barrier at the electron‐transporting layer, and relaxes the lattice strain to promote phase stability. Consequently, ambient printed CsPbI3 solar cells with power conversion efficiency as high as 20.01% under 1 sun illumination (100 mW cm−2) and 37.24% under indoor light illumination (1000 lux, 365 µW cm−2) are achieved; both are the highest for printed all‐inorganic cells for corresponding applications. Furthermore, the bare cells show an impressive long‐term ambient stability with only ≈5% PCE degradation after 1000 h aging under ambient conditions. A novel ionic liquid, 1‐ethyl‐3‐methylimidazolium hydrogen sulfate (EMIMHSO4), is employed for managing defects in printed cesium lead triiodide (CsPbI3) films. The EMIMHSO4 can succesfully regulate perovskite thin‐film growth and strongly coordinate with the undercoordinated Pb2+, which enable the achievement of the highest‐efficiencies ambient printed CsPbI3 solar cells, both under 1 sun illumination (20.01%, 100 mW cm−2) and indoor light illumination (37.24%, 1000 lux, 365 µW cm−2).