The current world demand for electricity has grown in the last decades, which has led to a boost in photovoltaic energy research. In the last few years a new type of solar cell, perovskite solar cell (PSC), has gained interest in photovoltaic community due to its high efficiency and low cost. Nowadays the most promising perovskite is the CH3NH3PbI3 that presents incredible efficiencies as high as 22.1%. However, it faces a problem concerning the commercial use due to its lead content and stability. In this way, new lead-free materials have been studied in the last few years. One of it is the lead-free perovskite-like material (CH3NH3)3Bi2I9 that can act as the absorption material in solar cells and has a better stability than CH3NH3PbI3. The precursor of this material is the bismuth triiodide (BiI3), a semiconductor material suitable as well for photovoltaic applications due to its optical bandgap of 1.67 eV [1, 2]. Usually BiI3 is made by solution processes  and in this work we compared BiI3 thin films obtained by this route with thermal evaporated BiI3 thin films. We used a spin coated solution of BiI3 in DMF:DMSO to make the solution process films and evaporation of BiI3 powder in a vacuum chamber with base pressure of 2 x 10-5 Torr to make thermal evaporated bismuth triiodide thin films. We estimated an indirect bandgap of 1.71 eV and 1.74 eV for bismuth triiodide thin films grown by thermal evaporation through ultraviolet-visible spectroscopy and photoluminescence measurements, respectively. We compared the morphology and crystallinity of BiI3 thin films grown by thermal evaporation and solution processes through scanning electron microscope images and x-ray diffraction measurements. The results indicate that the thermal evaporated thin films are smoother than the spin coating ones, which suggests that the bismuth triiodide thin films obtained by physical routes can be a better candidate for photovoltaic applications than the bismuth triiodide thin films obtained by solution methods.
Acknowledgements: CNPq, Capes, Fapesp, Lamult Unicamp.
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