Hierarchical Structure Design And Photoelectric Properties Of Photoanode For Quantum Dot Sensitized Solar Cells

Solar energy is a renewable energy with abundant reserves and wide distribution.It can convert light energy into electric energy by utilizing photovoltaic devices.Quantum dot sensitized solar cells?QDSSCs?have attracted widely attention due to their multi-exciton effect,adjustable band gap,low cost and high theoretical efficiency.However,the actual photoelectric conversion efficiency?PCE?of QDSSCs is still far from its theoretical PCE due to the low quantum dot?QD?loading amount,large electron transport resistance,severe interfacial charge recombination,and narrow light absorption range.Therefore,the improvement of the PCE of QDSSCs has become an important research topic in this field.Considering that photoanode is closely related to the process of light collection,electron injection and collection,this paper focus on the structure design of the photoanode.In order to solve the problems of low loading amount and serious interfacial charge recombination of quantum dots,a variety of photoanodes with hierarchical structures were designed and the influence of photoanode structure on the performance of QDSSCs was systematically analyzed.The main research contents and conclusions are as follows:?1?In order to simultaneously improve the specific surface area and electron transport efficiency of the photoanode,a bilayer-structured film with micro-flower TiO₂ as an overlayer and hierarchical porous TiO₂ as an underlayer is fabricated.The hierarchical porous TiO₂ nanoparticles increase the electron transport channels and the specific surface area of the photoanode.And TiO₂ micro-flower assembled from nanorods supplies abundant adsorption sites for CdSe quantum dots,thus leading to the enhanced light harvesting efficiency.In addition,the staggered band structure between the anatase nanoparticle and the rutile micro-flower will facilitate the separation of electron-hole pairs and promote the injection process of electron.Therefore,the PCE of QDSSCs based on double-layer photoanode is about 43%higher than that based on single-layer TiO₂ photoanode.?2?In order to improve the utilization of light and reduce the surface defects of ZnO,a photoanode with three-dimensional inverse opal?ZnO@ZIF-8 IO?structure is synthesized by self-assembled opal template method.Zn O@ZIF-8 IO photoanode has completely connected pores with extended diameter,thus promoting the permeability of QDs and electrolyte.Meanwhile,due to the slow photon and multi-scattering effect of the regularly interconnected macroporous array structure,the light harvesting ability and charge transport process can be enhanced.In addition,ZIF-8 shell coated on the surface of ZnO IO not only provides high porosity but also serves as a passivation layer thus reducing the carriers recombination occurred at the interfacial.The PCE of solar cells based on ZnO@ZIF-8 IO increased from 0.88%to 1.75%.?3?On the basis of?2?,TiO₂@NiO IO photoanode was designed in order to improve the light harvesting ability and promote electron transport process.TiO₂ IO photoanode was prepared by using TiO₂ as the IO skeleton,and the p-type oxide semiconductor NiO was introduced as the barrier layer to improve the potential barrier of charge recombination.Meanwhile,the formation of NiO barrier layer also increases the loading amounts of CdS/CdSe QD and improves the light absorption intensity in the visible region.The effect of NiO nanosheets and NiO nanoparticles as secondary structural units on the performance of QDSSCs was systematically studied,and the influence of NiO on charge transport process was deeply discussed.The photoelectric performance test results showed that the PCE of QDSSCs based on TiO₂@NiO IO photoanode increased 47%and reached 5.07%compared with that of QDSSCs based on TiO₂ IO photoanode.