Abstract
Dimethylformamide/dimethyl sulfoxide solvent mixtures were used as the CH3NH3PbI3 (MAPbI3) precursor solvent in a one-step spin coating method to fabricate smooth and hydrophilic crystalline MAPbI3 thin films on top of hydrophobic carbon-60 (C60) thin film for highly efficient photovoltaics. The structural, optical, and excitonic characteristics of the resultant MAPbI3 thin films were analyzed using X-ray diffraction (XRD), atomic-force microscopy, absorbance spectroscopy, photoluminescence (PL) spectrometry, and nanosecond time-resolved PL. There was a trade-off between the crystallinity and surface roughness of the MAPbI3 thin films, which strongly influenced the device performance of MAPbI3-based photovoltaics. The high power conversion efficiency (PCE) of 17.55% was achieved by improving the wettability of MAPbI3 precursor solutions on top of the C60 thin films. In addition, it was predicted that the fill factor and PCE could be further improved by increasing the crystallinity of the MAPbI3 thin film while keeping it smooth.
Highlights
High-quality organic lead halide perovskites (CH3NH3PbI3, CH3NH3PbI3−xClx, and CH(NH2)2PbI3), which can be fabricated using a two-step or a one-step spin-coating method [1,2,3,4], have been widely used as the light harvesting material in photovoltaic cells due to their high power conversion efficiency (PCE) and low-cost of fabrication
Smooth crystalline mixtures were used as the CH3NH3PbI3 (MAPbI3) thin films were first fabricated using a two-step solution process [1] with a porous PbI2 thin film used for the substrate, and a MAI thin film deposited on top of PbI2
Chlorobenzene, boromobenzene, and iodobenzene have been used as the anti-solvent in the washing treatment process while a mixture of gamma-butyrolactone (GBL) and dimethyl sulfoxide (DMSO), or a mixture of dimethylformamide (DMF) and DMSO was used as the MAPbI3 precursor solvent
Summary
High-quality organic lead halide perovskites (CH3NH3PbI3, CH3NH3PbI3−xClx, and CH(NH2)2PbI3), which can be fabricated using a two-step or a one-step spin-coating method [1,2,3,4], have been widely used as the light harvesting material in photovoltaic cells due to their high power conversion efficiency (PCE) and low-cost of fabrication. High-quality MAPbI3 thin films can be obtained using a one-step solution process with an in situ nonpolar antisolvent washing treatment [3,4,9]. The crystallinity of the resultant thin films was not high when DMF was used as the precursor solvent as it has a low boiling point (BP) of 153 ◦C. The roles of DMF and DMSO in the MAPbI3 precursor for regular-type perovskite photovoltaics were not completely understood in previous reports [26,27,28,29]. The aim of this study was to explore the interplay between nucleation and crystal growth during the formation of MAPbI3 thin films, and to investigate the influence of the properties (wettability and boiling point) of the precursor solvent on high-performance MAPbI3-based photovoltaics. Various volume ratios of DMF to DMSO were used as the MAPbI3 precursor solvent
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