Dual-source evaporation of silver bismuth iodide films for planar junction solar cells

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2019, Vol.7 (5), p.295-215
• Main Authors: Khazaee, Maryam, Sardashti, Kasra, Chung, Ching-Chang, Sun, Jon-Paul, Zhou, Hanhan, Bergmann, Eric, Dunlap-Shohl, Wiley A, Han, Qiwei, Hill, Ian G, Jones, Jacob L, Lupascu, Doru C, Mitzi, David B
• Format: Article
• Language: English
• Subjects: Biocompatibility; Bismuth; Electronics industry; Energy conversion efficiency; Energy dispersive X ray spectroscopy; Evaporation; Fabrication; Grain size; Iodides; Open circuit voltage; Particle size; Phase transitions; Photovoltaic cells; Photovoltaics; Pinholes; Scanning electron microscopy; Solar cells; Stoichiometry; Surgical implants; Temperature dependence; Titanium dioxide; X-ray diffraction; X-ray spectroscopy
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c8ta08679f

Non-toxic and air-stable silver bismuth iodide semiconductors are promising light absorber candidates for photovoltaic applications owing to a suitable band gap for multi- or single-junction solar cells. Recently, solution-based film fabrication approaches for several silver bismuth iodide stoichiometries have been investigated. The current work reports on a facile and reproducible two-step coevaporation/annealing approach to deposit compact and pinhole-free films of AgBi 2 I 7 , AgBiI 4 and Ag 2 BiI 5 . X-ray diffraction (XRD) in combination with scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX) analysis reveals formation of pure cubic ( Fd 3&cmb.macr; m ) phase AgBi 2 I 7 , cubic ( Fd 3&cmb.macr; m ) or rhombohedra ( R 3&cmb.macr; m ) phase AgBiI 4 , each with >3 μm average grain size, or the rhombohedral phase ( R 3&cmb.macr; m ) Ag 2 BiI 5 with >200 nm average grain size. A phase transition from rhombohedral to cubic structure is investigated via temperature-dependent X-ray diffraction (TD-XRD). Planar-junction photovoltaic (PV) devices are prepared based on the coevaporated rhombohedral AgBiI 4 films, with titanium dioxide (TiO 2 ) and poly(3-hexylthiophene) (P3HT) as electron- and hole-transport layers, respectively. The best-performing device exhibited a power conversion efficiency (PCE) of as high as 0.9% with open-circuit voltage ( V OC ) > 0.8 V in the reverse scan direction (with significant hysteresis). Dual-source evaporation approach is applied to deposit AgBi 2 I 7 , AgBiI 4 and Ag 2 BiI 5 films; a planar junction AgBiI 4 -solar cell is demonstrated.