Characterization of sequential physical vapor deposited methylammonium lead tri-iodide perovskite thin films

Methylammonium lead tri-iodide perovskite (MAPbI(3)) thin film for solar cells, chemical formula CH3NH3PbI3, is synthesized in situ via sequential thermal vapor deposition of lead(II)iodide (PbI2) and methylammonium iodide (MAI) single layers. The structural, morphological, optical, and electrical attributes are highly dependent on annealing time and MAI thickness. X-ray diffractograms confirmed the tetragonal crystal structure of MAPbI3 with I4/mcm space group, good crystallinity which increases with the thickness of MAI and transformation of PbI2-deficient MAPbI(3) to PbI2-rich MAPbI(3) upon increasing annealing time. UV-vis optical spectra reveal a redshift in the onset of absorption from 750 to 780 nm as the MAI thickness increases and a slight blueshift as the annealing time increases. Field emission scanning electron microscopy micrographs show densely packed polycrystalline grains with negligible pinholes and full coverage. The current density-voltage (J-V) characteristics under illumination reveals that the photogenerated current decreases with an increase in annealing time. Space charge limited current analysis of dark current J-V curves shows that PbI2-deficient MAPbI(3) has higher mobility than PbI2-rich MAPbI(3) and trap density increases with annealing time.