Perovskite Solar Cells Based On Quantum Dot Sensitized Inverse Opal Structure

Currently,in the important period of industrial revolution and economic transformation,innovation is needed for social development of China,of which new energy technology plays a crucial role.In addition,as traditional energy source is harmful to the environment,energy crisis is increasingly prominent.Therefore,it is urgent to find new and claen energy source.Environmentally friendly solar energy is considered as one of the most promising new energy sources because of many advantages such as large quantity and low cost.In recent years,organic-inorganic halide perovskite solar cells exhibit unprecedented development due to good properties of perovskites such as suitable direct bandgap,extra-long carrier diffusion length and high absorption coefficient.In order to solve the problem of thermal/humidity instability of perovskite solar cells,researchers turned their attention to all-inorganic perovskites,namely replaced organic ions with inorganic cesium ions(Cs+).On the other hand,the structure of inverse opal(IO)has aroused tremendous attention for its photonic band gap(PBG),which can lead to slow photon effect,prolong the optical path length,and hence remarkably enhance the light absorption ability and promote the carrier transport process.At the same time,quantum dots(QDs)themselves display advantageous properties,including high absorption coefficient,tunable bandgap by controlling the nanoparticle diameter,and low cost,which is conducive to the improvement of power conversion efficiency of perovskite solar cells.In this paper,photonic crystal structure and quantum dots are introduced into perovskite solar cells,along with systematically studied preparation and characteristics.The main contents are summarized as follows:(1)Olystyrene microspheres was prepared by emulsifier-free emulsion polymerization method.Inorganic CsPbBr2I 10 was prepared by sol-gel method as a light-absorbing material for perovskite solar cells.The morphological structure of CsPbBr2I IO was characterized by SEM.It is observed by UV that the presence of photonic crystals improves the light absorption capacity of the perovskite layer.This is because CsPbBr2I IO has an adjustable photon bandgap structure,which produces a slow photon effect that allows incident light to be scattered multiple times as it passes through the photonic crystal.Then,the large surface of the three-dimensional ordered microporous structure provides enough and orderly channels for the carrier transfer process.In addition,PbS quantum dots were prepared by hydrothermal synthesis with different energy levels by adjusting the size of PbS quantum dots.The performance of PbS quantum dots of different sizes was characterized by TEM and UV.To successfully combine the PbS quantum dots with the perovskite layer,ligand exchange method was used.The optical and electrical properties of the device were significantly improved because the narrow band gap and large Bohr radius of PbS quantum dots make strong light absorption in the near infrared region.Moreover,PbS quantum dots improved the band structure alignment,achieved photo-generated carrier balance,and facilitated the carrier extraction and injection.Through UPS,PL,TRRL,IPCE and other testing methods,the most suitable PbS quantum dot was selected and significantly improved the photoelectric conversion efficiency of perovskite solar cells.(2)PbSe quantum dots were prepared by hydrothermal synthesis to modify CsPbBr3.Through SEM and other testing methods,it was found that the PbSe quantum dots perfected the morphology of the perovskite layer.Through TRRL,IPCE and other methods,it was found that PbSe quantum dots effectively improved the light absorption performance.First,PbSe quantum dots promote nucleation and improve the coverage of perovskite film as well as passivate the surface of the light absorbing layer.Second,the quantum confinement effect and multi-exciton effect of PbSe quantum dots can generate more photo-generated carriers,thereby enabling more efficient electron transport and increasing the photo-generated current.In addtion,TiO2 mesoporous layer with inverse opal structure was prepared by soap-free emulsion polyrnerization method,and the process of filling and removing was reasonably controlled to maintain the integrity of the template which was proved by SEM.It was found by UV,PL and other tests that the mesoporous TiO2 improved the light absorbing performance because the existence of the photonic crystal structure improved the light absorption capacity of the solar cell.The excellent light capture ability of TiO2 IO film promotes the generation of photoexcited carriers and improves the light collection efficiency,resulting in stronger light absorption ability.Furthermore,the ordered and tightly interconnected framework of the TiO2 IO structure improves charge collection by effectively transmitting electrons,suppressing the recombination of electrons and holes.The improved transmittance of visible light wavelength enables more light to reach the perovskite layer.On this basis,perovskite solar cells were prepared.The results proved that after modification,both the light absorption ability of the light absorbing layer and the ability to separate and extract charges were improved,leading to higher photoelectric performance.