Evolutions of optical constants, interband electron transitions, and bandgap of Sn-doped CH3NH3PbI3 perovskite films

Abstract

CH3NH3PbI3 (MAPbI3) perovskite materials hold considerable promise for future low cost, high-efficiency solar cells, and replacement materials for toxic lead have also been in demand. In this study, the optical constants, absorption coefficients, and interband electron transitions of MAPb1−xSnxI3 (x = 0, 0.4, 0.8, and 1) films have been analyzed by spectroscopic ellipsometry in the photon range of 1 eV–5 eV. The bandgaps of MAPb1-xSnxI3 (x = 0, 0.4, 0.8, 1) are 1.54 eV, 1.51 eV, 1.49 eV, and 1.46 eV, respectively. With the increase in Sn, the s–p antibonding coupling becomes stronger, and the bandgap energy decreases, owing to the shallower and more active lone-pair states of Sn-5s than Pb-5s near the valence band maximum (VBM). According to the x-ray diffraction patterns, doping Sn does not change the material structures, which makes the shape of VBM more fluctuating, resulting in a similar band structure. Moreover, band structures and interband electron transitions of all four samples are discussed in terms of solid-state physics and can be assigned to the direct transition between the valence band and the conduction band at R, M, and X symmetry points.

Bi and Sn Doping Improved the Structural, Optical and Photovoltaic Properties of MAPbI3-Based Perovskite Solar Cells

“…The variation in “k” is due to doping, which refers to the change in the density of the film. This variation in “k” refers to a red shift, which is due to inter-band electronic transition when the Bi–Sn are co-doped in MAPbI 3 film [ 51 ]. The variation in inter-band electronic transition reflects the change in band structures, which confirms the substitution of Sn and Bi in the place of Pb in MAPbI 3 structures.…”

Effect of Structural Morphology and Material Factors on Radiative Properties of Hybrid Perovskite/Nanoporous GaN Hierarchical Composite Structure

“…The prominent absorption peak of ε 2 near 380 nm is red-shifted with the doped Sn elements. The reason is that MASnI 3 appears to have a stronger s – p antibonding coupling near the VBM than MAPbI 3 , which results in a higher VBM and, thus, a lower bandgap. The high electronegativity of the Sn element is also responsible for the optical absorption red shift .…”

“…The surface morphologies were then measured using AFM in tapping mode by HR Evo Nano (Figure b,c). The surface roughness was 95 ± 5 nm (RMS roughness), which is sufficient to meet SE requirements . Before ellipsometric measurement, the sample was cleaned with the model KQ5200SE ultrasonic machine to remove impurities.…”

“…The surface roughness was 95 ± 5 nm (RMS roughness), which is sufficient to meet SE requirements. 27 Before ellipsometric measurement, the sample was cleaned with the model KQ5200SE ultrasonic machine to remove impurities. Here, we prepared two electrochemically etched porous GaN films with pore sizes of 200 and 500 nm (see ref 31 for synthesis details) deposited on the sapphire.…”

“…We also consider the substitution of toxic element Pb in perovskite and further investigate the effect of Sn doping on spectral radiation properties. The optical constants of MAPb 1−x Sn x I 3 are obtained from SE measurements 27 (see Figure S11 in Supporting Information). The prominent absorption peak of ε 2 near 380 nm is red-shifted with the doped Sn elements.…”