Optimization Of The Photoanode Structure In Quantum Dot Sensitized Solar Cells

Quantum-dot Sensitized Solar Cell (QDSSC) has drawn extensive attention due to its low cost andhigh theoretical conversion efficiency which is considered to be an economic and efficient third generationsolar cell. In the configuration of QDSSC, photoanode can take an essential part in charge separation andtransport. Therefore, the photoanode structure is crucial to QDSSC photoelectric performance. The idealphotoanode should have1) high specific surface area which provides more nuclearation sites for quantumdots deposition with high coverage ratio;2) orderly assembled structures, which can provide efficientelectronic transport channel to facilitate the rapid transmission of photogenerated electron;3) goodscattering ability which could broaden the absorption range and maximum sunlight harvesting. In this thesisdesigned and prepared different structures TiO2and SnO2by solvethermal method and these products wereemployed as the photoanode materials in CdS/CdSe co-sensitized solar cell. Moreover, the effects of themicro/nanostructure on the QDSSC performances were studied in detail and possible influencingmechanisms were also proposed. The major works are listed as follow:(1) A unique graphene/TiO2composite structure was designed and prepared via a CTAB assistedsolvothermal method. The research shows that the reduced graphene oxide could be wrapped with highdensity TiO2nanocrystals with CTAB assistance(RGT-H). The RGT-H has a high quantum dots loadingamounts, high light scattering ability, which could effectively utilize incident light. In addition, with lowcharge carrier recombination and the gradient energy levels which could effectively restrain the reversediffusion of injection electrons. Therefore, the RGT-H based QDSSC shows a short-circuit current density(Jsc) of12.38mA cm-2, open circuit voltage (Voc) of569mV, and filling factor (FF) of57%, which resultsin a power conversion efficiency (PCE) of4.02%., indicating a~40%improvement compared with thenanocrystal cell (2.85%).(2) Multi-dimensional TiO2hierarchal structures (MD-THSs) assembled by1D mesoporousnanoribbons which consisted of oriented aligned0D nanocrystals were prepared via a simple hydrothermalmethod. The as-prepared TiO2hierarchical product was adopted as the photoanode material forquantum-dot sensitized solar cells using CdS/CdSe as co-sensitizers. It proves that photoanode with15μmthickness exhibits a Jscof14.39mA cm-2, Vocof561mV, and PCE of4.20%, which is~30%higher than the regular nanocrystals, the improved PCE is mainly result from that the MD-THSs have high specificsurface area (160m2g-1), wide pore size distribution (1-100nm) and oriented aligned primary anatasenanocrystals, which benefits the load of quantum dots, the electrolyte diffusion in the photoanode film andthe photoelectron transportation.(3) Different SnO2materials were prepared by a simple hydrothermal method and the growthmechanism was also studied. In addition, the research shows that the pH value could effectively control theassembly process of nanoparticles. By adjusting the NaOH dosages, SnO2rods, microspheres andnanoparticles could be selectively prepared. After TiCl4treatment, SnO2/TiO2composite photoanodesbased on different SnO2structures were used for QDSSC. It turned out that microspheres can effectivelybalance the specific surface area and the number of grain boundary in photoanode film, which can improvethe quantum dots loading amounts and guarantee the effective photoelectron transportation. Therefore, thePCE of the microsphere based QDSSC reach to1.61%, which indicates~65%and~46%improvementcompared with rods and nanoparticles, respectively.