Controlling Crystal Growth Of Non-Toxic Bismuth Iodide (Bii3) Semiconducting Material For Efficient Photovoltaics

High absorption coefficient, suitable band gap, and high electron mobility makes non-toxic 2D bismuth iodide (BiI3) a promising alternative to efficient, toxic perovskites and inorganic solar cells containing lead (Pb). In this work, we successfully synthesized, controlled, and optimized the crystal orientation of BiI3 crystals grown directly on a transparent conductive substrate using a custom-built close space sublimation (CSS) method. Morphology characterization by scanning electron microscopy (SEM) confirms the controlled morphology of Bib crystals. Record photoexcited carrier lifetime of 0.6 ns was characterized by time-resolved photoluminescence spectroscopy for the optimized vertical Bib crystals. The photoluminescence confirmed the band gap of the BiI3 film to be 1.82 ev which is a suitable band gap for photovoltaic application. The optimized vertical Bib crystals device showed a power conversion efficiency of 0.6% due to the fact that the optimized vertically oriented crystals allowed us to harness the high in-plane electron mobility of BiI3. Higher efficiencies can be obtained by further optimizing the electron and hole transport layers in our PV device. This work paves the way for controlling the orientation and morphology of Bib for efficient solar cells by using a facile, scalable, and transfer-free CSS method.