Composition tuning of CdSe_XS_1−X nanocrystals for enhancing the photovoltaic performance of CdS/CdSe_XS_1−X quantum dot-sensitized solar cells

In this work, CdSe_xS_1−x QDs with X different value and compositions were prepared for utilization as light absorbing in the CdS/CdSe_xS_1−x multiple quantum dot-sensitized solar cells. These QDs with X different value were deposited on the FTO/TiO₂NPs/CdS/CdSe_XS_1−X/ZnS photoanode through the successive ionic layer absorption and reaction (SILAR) method. Then the photovoltaic parameters were measured and extracted by different photovoltaic analyses. The X value was altered in the range of 0.1–0.4, and the corresponding cells were fabricated. According to the results, the best efficiency was achieved for the QDSCs with CdSe_XS_1-X, X = 0.3, light absorbing layer. The efficiency was increased about 39% compared to the reference CdSe_xS_1-x free cell. The process of synthesis and deposition of CdSe_XS_1-X QDs was carried out in 5 cycles. In the following, the number of SILAR cycles was optimized for the X appropriate ratio. According to measurements, the FTO/TiO₂NPs/CdS/CdSe_0.3S_0.7/ZnS photoanode structure with the CdSe_0.3S0_.7 layer deposited in 3 SILAR cycles, created and efficiency enhancement about 38% compared to the pervious maximum state. The IPCE curves were measured, and corresponding APCEs were extracted which showed a maximum quantum conversion efficiency about 75%, while the spectrum is spread in the wavelength range of 400–700 nm. This improvement in photovoltaic characteristics can be attributed to the broader light absorption region and higher light-harvesting efficiency. Besides, due to the performed calculations a cascade energy band diagram is formed between the CdS and CdSeS sensitizing layers which is suitable for well transfer of photogenerated electron–hole pair.