Deciphering the role of antisolvent on the structural and optical properties of CH3NH3PbI3 film and its impacts on the performance and stability of n-i-p perovskite solar cells

Abstract

This study presents an in-depth morphological, structural, and optical study of CH3NH3PbI3 (MAPbI3) film during the antisolvent dripping time, and their relevance to the stability and performance of perovskite solar cells (PSCs) is revealed. The detrimental role of the antisolvent is best demonstrated by using chlorobenzene (CB) as an antisolvent and comparing PSC devices fabricated from CB-free versus PSCs containing CB at different dripping times (5, 10, 15, 20, and 25 s) before the end of deposition of CH3NH3PbI3 film (deposition time was 30 s). Scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), UV–Vis absorption spectroscopy, Urbach energy analysis, steady-state photoluminescence (PL) spectra, current-voltage (I–V), external quantum efficiency (EQE), and water droplet contact angle measurement techniques were utilized to evaluate the characteristics of obtained MAPbI3 films, photovoltaic parameters, and the stability of constructed n-i-p PSCs. It was observed that changing the antisolvent dripping time changes the optical and structural properties of the MAPbI3 layer, including the direct and indirect optical band gap, refractive index, extinction coefficient, dielectric constant, optical conductivity, Urbach energy, dislocation density, lattice strain, crystallite size, and lattice parameters. The above-mentioned parameters were investigated in detail. Accordingly, by dripping the CB at 20 s before the end of the deposition process (labeled as a sample of 20 s), the created MAPbI3 layer had a smoother and pinhole-free surface, resulting in higher crystallinity than the other samples. The values of the direct band gap of the created MAPbI3 films varied from 1.51 to 1.61 eV, corresponding to samples CB-free and 20 s, respectively. For all samples, the indirect band gap was 60 meV lower than the direct band gap. Also, the sample at 20 s had a lower Urbach energy, indicating that this sample's interband defects are less than other models. In addition, the PSCs with CB-dripping at 20 s exhibited higher power conversion efficiency (13.95%) and outstanding stability of power output (<16% decay) as compared to the device without CB-dripping (>82% decay) after keeping in ambient air for about 1450 h at 40 ± 10% RH and 25 ± 5 °C. This systematic comparative study of the structural and optical properties of the perovskite layer can provide a promising platform for achieving high-quality perovskite films to overcome the shortcomings of instability and degradation.