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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SUMMARYThe strain compatibility documented in Chapter I of the American Institute of Steel Construction 360-10 (AISC, 2010) was modified to provide accurate analytical solution for hybrid composite precast beams. In the proposed method, locations of neutral axis of the section are investigated to formulate all possible equilibrium equations of stress fields of composite sections. The only neutral axis satisfying all stress fields is then found for composite sections for entire loading history including yield and maximum load limit state and between those limit states. Finally, the nominal moment capacity of hybrid composite precast beam is calculated based on the correct neutral axis. Experimental study was conducted to verify the accuracy of the proposed method. The test results for hybrid composite precast beams agreed very well with the analysis results. The capacity difference between them is less than 4.8%. This study also compares the proposed design method with the conventional strength addition method, showing that the conventional method underestimated structures leading to over-design. It was found that the new approach predicted the behaviors of hybrid composite precast beams more accurately than the conventional methods.

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