Recent studies have demonstrated that copper (I) thiocyanate (CuSCN) has huge potential as a hole extraction material (HEM) for perovskite solar cells. Here, we used CuSCN as a HEM and analyzed its relationships with a methylammonium lead iodide (MAPbI 3 ) perovskite layer. The CuSCN dissolved in diethyl sulfide (DES) was spin-coated on the MAPbI 3 layer. For high-quality and dense CuSCN layers, post-annealing was carried out at various temperatures and times. However, the unwanted dissociation of MAPbI 3 to PbI 2 was observed due to the postannealing for a long time at elevated temperatures. In addition, DES, which is used as a CuSCN solvent, is a polar solvent that damages the surface of MAPbI 3 perovskites and causes poor interfacial properties between the perovskite layer and HEM. To solve this problem, the effect of the molar ratio of methylammonium iodide (MAI) and PbI 2 in the MAPbI 3 precursor solution was investigated. The excess MAI molar ratio in the MAPbI 3 precursor solution reduced MAPbI 3 surface damage despite using DES polar solvent for CuSCN solution. In addition, dissociation of MAPbI 3 to PbI 2 following an adequate post-annealing process was well suppressed. The excess MAI molar ratio in the MAPbI 3 precursor could be compensated for the MA loss and effectively suppress phase separation from MAPbI 3 to MAI + PbI 2 during post-annealing. The efficiency based on the normal planar structure of CuSCN/MAPbI 3 (using excess MAI)/TiO 2 was approximately 17%. The CuSCN-based MAPbI 3 device shows more optimized stability than the conventional spiro-OMeTAD under damp heat (85 °C and 85% relative humidity) conditions because of the robust inorganic HEM.

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We have investigated the charge collection condition around voids in copper indium gallium sulfur selenide (CIGSSe) solar cells fabricated by sputter and a sequential process of selenization/sulfurization. In this study, we found direct evidence of void passivation by using the junction electron beam induced current method, transmission electron microscopy, and energy dispersive X-ray spectroscopy. The high sulfur concentration at the void surface plays an important role in the performance enhancement of the device. The recombination around voids is effectively suppressed by field-assisted void passivation. Hence, the generated carriers are easily collected by the electrodes. Therefore, when the S/(S + Se) ratio at the void surface is over 8% at room temperature, the device performance degradation caused by the recombination at the voids is negligible at the CIGSSe layer.

Sulfur is extensively used to increase the bandgap of Cu(In,Ga)(S,Se)2 (CIGSSe) solar cells and to improve the open circuit voltage (VOC) in order to optimize the characteristics of the devices. This study uses a sulfurization process to obtain a double‐graded bandgap profile. Selenization was carried out on Cu(In,Ga) precursors, followed by one sulfurization process or two consecutive sulfurization processes on top of the CIGSe absorber layer surface. The optimum two‐step sulfurization process provides an increase of VOC of 0.05 V and an improvement of conversion efficiency of 1.17%. The efficiency of the 30 × 30 cm2 monolithic module, which has 64 CIGS cells connected in series (aperture area: 878.6 cm2), is 15.85%. The optical and electrical properties of the phase and the work function distribution were investigated using the depth profiles of the absorber layer as a function of the sulfurization conditions. The CIGSSe thin film formed by two‐step sulfurization with a high sulfur concentration exhibits a single work function peak, better crystallinity, and higher conversion efficiency than those of the thin film formed by two‐step sulfurization at low sulfur concentration. In terms of the Raman spectra depth profile, the phase areas for the CIGSSe thin film that underwent the optimized high sulfur concentration two‐step‐sulfurization appeared to have less of Cu2‐xSe phase than that with low sulfur concentration. Consequently, surface and interface phase analysis is an essential consideration to improve cell efficiency. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.