The Study Of Solid-State Quantum Dot Solar Cells Based On Composite Cds-ZnS Quantum Dots

Solar cells are important means to solve the increasingly serious problem of energy depletion and environmental issues, which attract widespread attention in recent years. Among different solar cells, quantum dot solar cells have the advantages of low cost, good stability and long life. Moreover, the theoretical power conversion efficiency（η） can reach to 66% owing to the quantum effects, leading to that it has great application prospects, which attract much researchers’ attentions. But the efficiency of quantum dot solar cells is still remaining low, especially for solid-state quantum dot sensitized solar cells（QDSSCs）. The main reasons rely not only on the low deposition amounts of quantum dots but also on the severe recombination between electrons and holes at the interfaces. In order to suppress recombination, some measures must be taken such as inserting a passivation layers between photo-anode and hole transport layers（HTL） to prevent the recombination of charge carriers, which can improve the efficiency of quantum dot sensitized solar cells.Our thesis fabricated CdS quantum dots sensitized solar cells. First of all, we get an efficiency of 0.33% through optimization of every procedure in fabricating pure solid state CdS quantum dots sensitized solar cells. Afterward, the efficiency improve to 0.42% through fabricating a conventional recombination barrier structure, in which ZnS blocking layers are deposited after CdS QDs（denoted as CdS/ZnS）. However, passivation layers may inhibit the transfer of charge carriers if their thickness exceeds the proper range, thus leading to the decreased efficiency. Herein, we provide a new method to suppress charge recombination in solid-state QDSSCs. The composites of ZnS and CdS QDs with different ratios are adsorbed on nanostructured TiO₂ surfaces（denoted as CdS-ZnS）, in which CdS and ZnS act as QDs sensitizer and blocking material, respectively. With the increase of ZnS, the recombination impedance at the TiO₂/HTL interface could be enhanced, leading to a longer electron lifetime（τ_n）, higher short current(J_SC) and power conversion efficiency（η）; An excess of ZnS, however, will cause losses in photocurrent and decrease in η, A combination of 83% CdS-17% ZnS gives the highest efficiency（0.68%）, which is significantly higher than the case of pure CdS（0.33%）. Compared with the conventional recombination barrier structure CdS/ZnS device, the CdS-ZnS based device shows much higher recombination impedance, which is more advantageous to suppress the electrons-hole recombination and increase τ_n, resulting in a higher J_SC, fill factor（FF） and open-circuit voltage(V_OC) and thus higher η.