Tailoring the film morphology and interface band offset of caesium bismuth iodide-based Pb-free perovskite solar cells

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2019, Vol.7 (27), p.8335-8343
• Main Authors: Khadka, Dhruba B, Shirai, Yasuhiro, Yanagida, Masatoshi, Miyano, Kenjiro
• Format: Article
• Language: English
• Subjects: Annealing; Bismuth; Cesium; Crystal growth; Energy conversion efficiency; Lead free; Material properties; Morphology; Open circuit voltage; Optoelectronics; Organic chemistry; Perovskites; Photoelectrons; Photovoltaic cells; Raman spectra; Scanning electron microscopy; Solar cells; Solvents; Thin films; Toxicity; X ray photoelectron spectroscopy
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/c9tc02181g

Bismuth-based halide perovskites (Bi-HaP) are low toxicity and air-stable materials with promising photo-absorber properties. In this study, we fabricated Bi-HaP (Cs 3 Bi 2 I 9 and CsBi 3 I 10 ) films by a solution process followed by solvent annealing and investigated the crystal growth and optoelectronic properties of these materials. A compact and large grain morphology of the Bi-HaP films was realized by annealing under ambient solvent vapor conditions. Collective analysis of XRD patterns, and Raman spectra, absorption and PL spectra of the fabricated films corroborates that the Cs 3 Bi 2 I 9 film ( E g ∼ 2.08 eV) with a hexagonal crystal phase is more stable under annealing conditions in a wide temperature range and ambient solvent vapor annealing conditions as compared to the other CsBi 3 I 10 thin film, having the narrower E g ∼ 1.8 eV, of the Bi-HaP family. We have achieved the best power conversion efficiency as high as ∼1.26% with the open circuit voltage of 0.74 V for the device fabricated with Cs 3 Bi 2 I 9 . The analysis of material properties and device characteristics indicates that morphology tailoring, surface chemistry control, and interface band offset engineering are important for the further improvement of Bi-HaP-based devices. Antisolvent treatment followed by solvent vapor annealing affected the morphology of the caesium bismuth halide film and impacted the device parameter tuning by the carrier transport layer.