Interface Modification And Performance Optimization Of Polymer-Nanocrystals Hybrid Solar Cells

Solar energy has always been regarded as an important way to solve the global energy crisis.Solar cells are an effective means to realize the rapid conversion of solar energy into electrical energy.After decades of development,the third generation solar cells based on solution-processed technology are still hot research topics.The polymer-nanocrystals hybrid solar cells have extremely important research and application prospects,due to the combination of flexibility,easy processing,high extinction coefficient of polymers and width absorption range,high mobility and high stability of nanocrystals.However,owing to the difficulty in phase separation control between polymer and inorganic nanocrystal and the existence of surface defects of nanocrystal,these complex interfaces in hybrid solar cells greatly reduce the charge separation and transport efficiency,thus limiting the device performance.This paper mainly focuses on the modification of interface properties in polymer-nanocrystals hybrid solar cells.A series of innovative researches have been carried out for modification of the nanocrystal surface and the interface between polymer and nanocrystals.We reveal the effects of Cl ions on the photophysical properties of CdTe nanocrystals,the device performance of hybrid solar cells and the carrier dynamics.Then,a record power conversion efficiency of 5.9%is achieved based on the improved device structure.Finally,we develop a method to passivate the surface defects of CsPbI₂Br perovskite nanocrystals,and obtain record power conversion efficiency of 12%and open-circuit voltage of 1.3 V based on polymer-nanocrystals planar heterojunction solar cells.Three detail aspects are introduced in the following paragraphs.1.In chapter II,water-soluble poly?p-phenylene-vinylene??PPV?precursors and CdTe nanocrystals with different Cl content are synthesized and applied in the hybrid solar cells.The effects of Cl on the photophysical properties of CdTe nanocrystals,crystal growth,defect passivation,photocarrier dynamics and device performance are systematically investigated.We demonstrate that the surface trap states of CdTe nanocrystals can be effectively passivated by Cl ions,and Cl in the CdTe nanocrystals can promote CdTe grain growth in the sintered process to reduce grain boundaries,thus facilitating charge transport.The power conversion efficiency of the hybrid solar cells based on CdTe nanocrystals with optimal Cl content reaches 5.25%.2.In chapter III,we improve the device structure of aqueous-processed hybrid solar cells.Polymer/CdTe planar heterojunction solar cells with optimized band alignment are constructed,which result in reduced interface charge recombination,enhanced carrier collection efficiency and built-in field.Finally,a champion power conversion efficiency of 5.9%,which is a record for aqueous-processed solar cells based on CdTe nanocrystals,is achieved after optimizing the photovoltaic device.3.In chapter IV,we use the similar device structure of chapter III and report an effective method of modifying the interface between a CsPbI₂Br absorber and polythiophene hole-acceptor to minimize the energy losses(E_loss).Cesium-based trihalide perovskites have been demonstrated as promising light absorbers for photovoltaic applications due to its superb composition stability.However,the large E_loss has become a major hindrance impairing the ultimate efficiency of inorganic perovskite solar cells.We demonstrate that polythiophene passivation of surface defect states.In addition,the interface properties are improved by a simple annealing process,leading to significantly reduced energy disorder in polythiophene and enhanced hole-injection into the hole-acceptor.Consequently,one of the highest power conversion efficiency of 12.02%in stable inorganic mixed-halide perovskite solar cells is obtained.Modifying the perovskite films with annealing polythiophene enables an open-circuit voltage of up to 1.32 V,which is the highest value reported among cesium-lead mixed-halide perovskite solar cells.The energy losses of 0.5 eV is one of the lowest voltage deficits reported among inorganic perovskite photovoltaics to date.In summary,this paper focuses on the interface modification of polymer-nanocrystal hybrid solar cells.By optimizing the surface properties of nanocrystals and the interface properties between polymer and nanocrystals,efficient charge transport and charge transfer are achieved,and thus the device performance is improved step-by-step.This paper has important reference to the development of polymer-nanocrystal hybrid solar cells and the understanding of the interface properties in solar cells.