The effects of high-temperature (500 °C) post-deposition annealing (PDA) on the properties of cesium lead bromide (CsPbBr3) films deposited by vacuum evaporation were studied. The PDA effectively improved the grain size of the CsPbBr3 films. This improvement of the grain size leads to the improvement of carrier diffusion length from 0.1 µm to 0.5 μm. A CsPbBr3 solar cell fabricated using a CsPbBr3 layer with PDA at 500 °C for 60 min showed a conversion efficiency of 6.62% (VOC = 1.465 V, JSC = 6.57 mA/cm2, and FF = 0.688). Our CsPbB3 solar cell also showed a conversion efficiency of 22.5% (VOC = 1.502 V, JSC = 53.7 mA/cm2, and FF = 0.574) for blue LED light (peak wavelength of 453 nm) with an intensity of 206 mW/cm2.
To develop polycrystalline thin-film tandem solar cells, a SrCuSeF/In2O3:Sn (ITO) bilayer film was studied. The transparent p-type conductive SrCuSeF layer was deposited by pulsed laser deposition (PLD), and the n-type conductive ITO layer was deposited by RF sputtering. The SrCuSeF/ITO bilayer film showed ohmic I–V characteristics. A tunnel junction between the p-type SrCuSeF and n-type ITO layers was successfully formed because the p-type SrCuSeF and the n-type ITO layers had sufficiently high carrier concentrations. The SrCuSeF/ITO bilayer film was applied as the back contact of a CdS/CdTe solar cell. The photovoltaic performance of the CdS/CdTe solar cell depends considerably on the thickness of the SrCuSeF layer. The CdTe solar cell with a back contact of the SrCuSeF layer with a thickness of 34 nm and the ITO layer with a thickness of 200 nm showed a high conversion efficiency of 14.3% (VOC = 804 mV, JSC = 27.5 mA/cm2, and FF = 0.65). The conversion efficiency was much higher than that of the CdTe solar cell with the SrCuSeF single-layer back contact (11.6%) and that of the CdTe cell with the ITO single-layer back contact (2.75%).
Substrate-type CdTe thin-film solar cells with a carbon/CdTe/CdS/ZnO:Al/Ag structure were fabricated. For promoting the formation of the CdSxTe1-x mixed crystal layer in the CdS/CdTe interface, the heat treatment (a face-to-face annealing at 600 °C and the second CdCl2 treatment at 415 °C) of the CdS/CdTe:Cu structure was performed after the CdS deposition. Junction photoluminescence and the compositional depth profile revealed that the CdSxTe1-x mixed crystal layer was formed in the CdS/CdTe interface as a result of the heat treatment after the CdS deposition. The cell performance was slightly improved due to the heat treatment after the CdS deposition, but the conversion efficiency remained low (less than 2%), probably due to the decrease in the acceptor concentration in CdTe layer. For improving cell performance, Cu diffusion was performed after the heat treatment of the CdS/CdTe structure (second Cu doping), in addition to the Cu doping before the CdS deposition (first Cu doping). The conversion efficiency increased with increasing Cu concentration in the second Cu doping, and approximately 10% efficiency was achieved.
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