Charge recombination is an important factor that limits the cell efficiency of quantum dot sensitized solar cells (QDSSCs). Herein, we report a facile way to improve the cell performance of CdSe sensitized ZnO QDSSC by overcoating a thin layer of ZnSe on CdSe/ZnO film through a successive ionic layer adsorption and reaction (SILAR) procedure. Photovoltaic investigations indicate that ZnSe overcoating can increase photocurrent and photovoltage of the cell, resulting in significant enhancement of the cell efficiency, which is much better than the widely used traditional ZnS material. The superior role of ZnSe overcoating is ascribed to its large inhibition of charge recombination loss owing to its suitable band structure, efficient passivation of ZnO and CdSe QDs as well as its small lattice mismatch with CdSe that leads to the large decrease of surface/interface defects in CdSe/ZnO photoanode . This finding provides an alternative efficient way to enhance the cell performance of ZnO based QDSSC by suppressing the charge recombination.
TiO 2 nanocrystals are widely used in photoanodes for quantum dot solar cells (QDSCs) owing to their chemical stability and suitable energy band structure. However, surface defects and grain boundaries of TiO 2 nanocrystals photoanodes allow high surface charge recombination, which limits the performance of QDSCs. In this work, an ultrathin TiO 2 layer is introduced to the surface of TiO 2 photoanodes by atomic layer deposition (ALD). The ultrathin layer not only reduces the surface defects of TiO 2 nanoparticles and strengthens the connection between adjacent nanoparticles to suppress the charge recombination for improving the electron collection efficiency (η cc ), but also increases the surface energy of photoanodes to load more quantum dots (QDs) for enhancing the light harvesting efficiency (LHE). As a result, the solar cell based on CdS/CdSe QDs with ALD treatment exhibits an efficiency of 5.07% that is much higher than that of the cells without modification (4.03%).
Yitan Li,Lin Wei,Cuncun Wu,Chang Liu,Yanxue Chen,Hong Liu,Jun Jiao,Liangmo Mei
Uniform zinc oxide (ZnO) nanosheet arrays were grown on woven titanium wires using a low temperature hydrothermal method. Photoanodes were prepared by depositing CdS and CdSe quantum dots onto the ZnO nanosheet arrays by a successive ionic layer adsorption and reaction (SILAR) method. Solar cells were assembled using these nanostructured photoanodes and their photovoltaic performance was characterized. The effect of using SILAR cycles for the deposition of quantum dots on the performance of these nanostructured solar cells was investigated systematically. The overall light-to-electricity conversion efficiency of 0.98% was achieved under 100 mW cm−2 illumination for flexible CdS/CdSe co-sensitized solar cells using conventional Pt foils as counter electrodes. To further improve the performance of the flexible solar cells, PbS and Cu2S counter electrodes based on Pb and Cu foils were fabricated. The best conversion efficiencies of flexible CdS/CdSe co-sensitized solar cells using Cu2S and PbS counter electrodes were 3.4% and 2.5%, which demonstrated a significant enhancement in values for short circuit current, open circuit voltage, and fill factor compared to those obtained with the commonly used Pt and Au electrodes.
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