The physical properties of bismuth replacement in lead halogen perovskite solar cells: CH3NH3Pb1-xBixI3 compounds by ab-initio calculations
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The selection of elements used in the design of solar cells is crucial in terms of environmental pollution and legalization problems due to the fact that both solar energy conversion efficiency as high as possible and toxic effects when dissolved in water. Hybrid Pb halogen solar cells demonstrate promising solar cell conversion material properties with a conversion rate of approximately 20%. However, Pb is a toxic element when dissolved in water. In this study, it was aimed to design new material forms for solar cells obtained by replacing Pb with a less toxic element without disrupting the photophysical properties of the material. This approach has been exemplified by focusing on bismuth considering Goldschmidt rules (GRs), Tolerance factor concept (t) and Shockley Queisser (SQ) limits. Non-stoichiometric CH3NH3Pb(1-x)Bi(x)I3 crystal structure were formed at the ratios determined by x = 0.125, 0.25, 0.75 and 1.00 values by replacing Bi3+ with Pb2+. Using the Density Functional Theory (DFT), the effect of added Bismuth ions in the structural and electronic properties of the material was investigated. According to the Shockley Quisser (SQ) limit, the crystal form CH3NH3Pb0.875Bi0.125I3 formed with x= 0.125 ratio was determined to be the most suitable structure in terms of solar cell productivity with a direct band gap of 1.30 eV. In addition, the band gaps of CH3NH3Pb0.500Bi0.500I3 and CH3NH3Pb0.250Bi0.750I3 formed at x= 0.50 and 0.75 were calculated to be 1.0863 eV and 1.0895 eV, respectively. Band gaps of these phases were also within the SQ limit. However, the band gap of the CH3NH3PbI3 stoichiometric phase was calculated to be 1.6826 eV above the SQ limit, while the CH3NH3BiI3 phase band gap was calculated to be 0.2738 eV well below the SQ limit. According to our DFT calculations, organic halogen perovskite compounds in the form of CH3NH3Pb(1-x)Bi(x)I3 formed at ratios of x = 0.125, 0.50 and 0.75 have been found to be more efficient than CH3NH3PbI3 compounds in terms of solar energy conversion capacity, optoelectronic systems and environmental safety.