Precipitation of CH₃NH₃PbCl₃in CH₃NH₃PbI₃and Its Impact on Modulated Charge Separation

Abstract

A precipitation of CH 3 NH 3 PbCl 3 (MAPbCl 3 ) in CH 3 NH 3 PbI 3 (MAPbI 3 ) has been observed for deposition from solutions containing CH 3 NH 3 I (MAI), PbCl 2 and small amounts of ammoniumvaleric acid iodide (HOOC-(CH 2 ) 4 NH 3 I or AVAI) in N,N-dimethylformamide. The influence of the precipitation of MAPbCl 3 on the electronic properties of the free perovskite layer and of the nanoporous TiO 2 /perovskite nanocomposite has been investigated by modulated surface photovoltage spectroscopy. The lowest characteristic energy of exponentially distributed defect states below the band gap was found for the highest amount of AVAI in the solution (2.6% for the given experiments). Stabilization of MACl by AVA and the role of coadsorption of ions on TiO 2 surfaces for charge separation and layer formation are discussed on the basis of interaction and adsorption energies obtained by molecular modeling.

Investigation of Structural and Electronic Properties of CH3NH3PbI3 Stabilized by Varying Concentrations of Poly(Methyl Methacrylate) (PMMA)

“…This might be correlated to the presence of PbI 2 [21] as detected in the GIXRD measurements (see also Supplementary Information Figures S1 and S2). For perovskite coated with 20 mg/mL of PMMA, the in-phase signal was positive while the phase shifted by 90 • signal was negative, indicating one mechanism of charge separation [24]. Positive in-phase signal has a maximum height of 0.51 mV at 1.7 eV and for the sample coated with 40 mg/mL of PMMA, both in-phase and phase shifted by 90 • signals are positive, showing two mechanisms of charge separation.…”

“…This suggests that trapping and de-trapping of charge carriers may lead to a slow response of the SPV spectra [18]. Since in-phase and phase shifted by 90 • signals had the same signs, charge separation was caused by the two mechanisms of charge separation and that relaxation of SPV signals was due to recombination processes [24]. Figure 3 represents the GIXRD patterns of the Mo substrate coated with 40 mg/mL of PMMA and of CH 3 NH 3 PbI 3 deposited onto the Mo substrate and thereafter coated with PMMA at concentrations of 0, 20, 40 and 80 mg/mL for the as-deposited sample measured on the day of preparation.…”

“…Furthermore, SPV is very sensitive at low light intensities where charge separation takes place [18]. SPV can be used to study exponential defect states below the band gap of CH 3 NH 3 PbI 3 and previous studies showed that the addition of a small amount of ammoniumvaleric acid iodide (AVAI) into solution containing CH 3 NH 3 I and PbCl 2 leads to a reduction in the value of defects below the band gap, and hence a reduction in the disorder in the material [24]. The study provides a better understanding of the electrical and structural behavior of CH 3 NH 3 PbI 3 coated with PMMA to promote development of stable related photovoltaic devices.…”

A Surface Photovoltage Study of Surface Defects on Co-Doped TiO2 Thin Films Deposited by Spray Pyrolysis

“…The height/yield of the RBS signal is proportional to the amount of material present in the sample, and it depends on the scattering cross-section of the detected element. The width of the peak is proportional to the thickness of the probed sample and depends on the energy loss per unit depth of the detected element [26].…”

“…The width of the peak is proportional to the thickness of the probed sample and depends on the energy loss per unit depth of the detected element [26]. A decrease in the width of the RBS signals from Ti and Co and a shift of the signal from the surface of the c-Si substrate to higher channels was observed with an increase in the amount of CoCl2 in the precursor solution.…”