Application Of Novel Morphology Control Strategy In All-small-molecule Organic Solar Cells

Solar energy has always been considered as the cleanest and most abundant renewable energy,and people are also using a variety of technologies to make use of it,such as photoelectricity,photothermal,photocatalysis,etc.The most widely used form of solar energy is photoelectric conversion.In the photovoltaic industry,the vast majority of the market share is occupied by silicon-based photovoltaic cells.However,the precision purification and doping required in the preparation process of silicon-based photovoltaic cells greatly increase the production cost.In addition,silicon-based solar cells are not suitable for making flexible devices.At present,most of the academic development of solar cell technology focuses on the production process of simpler third generation photovoltaic cells.These solar cells can be prepared using the solution method and can then be produced by roll-to-roll printing,which simplifies the manufacturing process and reduces costs.Among them,organic solar cells have advantages that traditional siliconbased solar cells do not have,such as solution preparation,flexible devices can be prepared,easy to modify materials,etc.Therefore,organic solar cells have been developing rapidly in recent years.Organic solar cells can be divided into whole small molecule solar cells and polymer solar cells.Currently,polymer solar cells have achieved a maximum photoelectric conversion efficiency of more than 18%.In contrast,the photoelectric conversion efficiency of all-small molecule solar cells has just exceeded 15%,and the development is relatively slow.It is not only inferior in photoelectric conversion efficiency,but also worse in performance stability.However,the differences between batches of polymer materials still cannot be effectively resolved.Small molecular materials have more definite chemical structure,more definite molecular weight size and easy to adjust the photoelectric properties,so quickly become a new research hotspot.Total small molecule organic solar cells have unique advantages,but also a relatively obvious disadvantage:low photoelectric conversion efficiency.The improvement of photoelectric conversion efficiency can be solved in many ways,such as the development of new donor and acceptor materials,the development of morphologic control strategies of active layer and interface modification.Moreover,the cell morphology of total small molecule organic solar energy is sensitive to experimental conditions,which means that it is difficult to accurately regulate it to achieve optimal carrier transport.In order to solve the difficult problem of precise morphology control of total small molecule solar cells,this paper firstly introduced volatile solid additives into total small molecule organic solar cells and adopted a new morphology control strategy of dimer donor materials,and applied it to improve the morphology of active layer,so as to improve the photoelectric conversion efficiency.First,a novel donor receptor combination of BTR-Cl:N3 was adopted,and a series of process optimizations were carried out to achieve the high efficiency of current allsmall molecule organic solar cells,and it was used as a standard device.Secondly,a novel volatile solid additive,IC-Fi,which has a chemical structure similar to the terminal group of representative non-fullerene receptors,was introduced and applied to the BTR-Cl:N3 system.The intrinsic structural characteristics of IC-IF enable the receptor material N3 to self-assemble and enhance the mixing of BTR-Cl and N3 during subsequent thermal annealing.This provides nanoscale phase separation and the accumulation of major face-on molecules within the blend membrane,which facilitates the charge transfer and extraction process in the device.The photoelectric conversion efficiency(PCE)of the device is increased from 13.36% to 14.43%,and the filling factor(FF)is increased from 64.7% to 73.5%.The results show that the use of volatile solid additives is a targeted,simple and practical strategy to control the morphology of the active layer of all small molecule organic solar cells.Finally,a new donor material,DBTR-Cl,was used to fabricate the device with star material Y6 as the acceptor.By fine-tuning the donor material of the active layer,the morphology of the active layer can be accurately controlled.After a series of optimizations,the results show that the photoelectric conversion efficiency of the device is 13.17% when using BTR-Cl as the donor.However,the photoelectric conversion efficiency of the device is improved to 14.39% after using the modified new material of BTR-Cl as the donor.The main performance parameter was the filling factor(FF),which increased from 65.90% to 70.76%.In this paper,in addition to the new donor receptor combination BTR-Cl:N3,two novel morphology control strategies,namely volatile solid additive and dimer donor material,were applied to the total and small molecule organic solar cells based on BTRCl donor,respectively,to carry out targeted morphology control for specific systems and obtain higher device performance.It provides a direction for the precise regulation of the morphology of all-small molecule organic solar cells in the future.