Calculation and Fabrication of a CH 3 NH 3 Pb(SCN) x I 3−x Perovskite Film as a Light Absorber in Carbon-based Hole-transport-layer-free Perovskite Solar Cells

CH3NH3Pb(SCN)xI3−x films were prepared using a hot-casting method with five different Pb(SCN)2/PbI2 levels (x = 0, 0.25, 0.5, 1 and 2). Substitution of SCN− in the CH3NH3PbI3 structures induces a film color transformation from black to yellow. UV vis spectra of CH3NH3Pb(SCN)xI3−x films display an increased band gap from 1.59 eV (pure CH3NH3PbI3 film) to 2.37 eV (MAPb(SCN)2I films). Experimental XRD spectra of CH3NH3Pb(SCN)xI3−x films for increasing SCN− levels show a reduced angle of the (110) plane in the same trend as for the simulated tetragonal CH3NH3Pb(SCN)xI3−x structures. The calculated bandgap of simulated tetragonal CH3NH3Pb(SCN)xI3−x structures also increases with the SCN− concentration. Maximal efficiency, 4.56%, was gained from a carbon-based hole-transport layer (HTL)-free CH3NH3PbI3 (x = 0) perovskite solar cell. This is attributed to the low bandgap of CH3NH3PbI3 (1.59 eV). Although, the efficiency of the carbon-based HTL-free CH3NH3Pb(SCN)xI3−x solar cells decreases with increasing SCN− ratio, the excellent solar cell stability was obtained from carbon-based HTL-free CH3NH3Pb(SCN)xI3−x (x = 0.25, 0.5, 1 and 2) solar cells. This should be influenced by the presence of the hydrogen bonds between H and S and/or H and N in the CH3NH3Pb(SCN)xI3−x structures. The carbon-based HTL-free CH3NH3Pb(SCN)0.5I2.5 solar cell delivers a promising efficiency of 3.07%, and its efficiency increases by 11.40% of its initial value after 30-day storage.