Research On Improving The Performance Of Polymer Organic Solar Cells Based On A Layer-by-Layer Deposition Method

Organic solar cells（OSCs）have been widely concerned by researchers due to their unique advantages of light,soft,thin,transparent and high-throughput solution roll-to-roll processing.The photovoltaic performance of solution-processed organic solar cells,including device efficiency and stability,is closely related to the microstructure of the bulk-heterojunction（BHJ）blend of a specific photoactive material system.In recent decades,BHJ solution solutioning-technology has played an irreplaceable leading role in the development of OSCs,and its performance has made great progress.However,the optimal nanoscale morphology of BHJ active layer is difficult to achieve and is highly sensitive to processing conditions and material properties.Finding effective morphology control methods is still one of the important research issues.Based on this point,this thesis systematically evaluated multiple target parameters from the construction of high-performance OSC photovoltaic devices by a Layer-by-Layer（Lb L）processing method,and successfully used this method to overcome the scaling lag of devices efficiency,and prepared high-performance large-area organic solar modules with high coating speed.The main contents are as follows:（1）In this chapter,five Lb L organic solar cells based on PTQ10 and J71 as the donors and ITC6-IC,IDIC,Me IC,ITCPTC and ITIC as the non-fullerene acceptors were fabricated with a single solvent（chloroform）and a Lb L deposition technique without preconditioning（such as mixed solvents and additives）.Compared with the devices based on a BHJ structure,these five systems showed higher or comparable photoelectric conversion efficiencies.The Lb L deposition method is not only suitable for the spinning coating process,but also for the blade-coating process which is close to the roll to roll production.The large area（1 cm²）OSC devices were prepared by the Lb L solution blade-coating technology in air environment,and the optimal power conversion efficiency（PCE）was more than 10%.（2）The two processing strategies of BHJ and Lb L are further compared by a blade-coating technology on account of the properties of the devices fabricated from the BHJ and Lb L active layer structures are different.Based on the device performance results,multiple target parameters are systematically evaluated.First,the real-time morphology evolution of the film formation process was monitored,and the differences of the surface and vertical morphologies of the films were compared.Through independent control and optimization of the Layer-by-Layer deposition of the donor and acceptor,Lb L blade-coating was conducive to obtain thermodynamically more favorable nanotopography and appropriate acceptor interface region.Secondly,the optics and device physical dynamics are analyzed.It was found the 3D geometric structure of the active layer prepared by Lb L balde-coating can achieve higher light absorption capacity.The appropriate blending morphology and interface between donor and acceptor can reduce carrier recombination and improve charge transport properties.Final,the Lb L-type active layer has more stable morphology,and the corresponding device exhibits better photostability and thermal stability,as well as mechanical stability.（3）The morphology of the active layer of BHJ structure is difficult to be controlled in large-scale fabrication.According to the above comparison of the active layer and device based on BHJ and Lb L structures prepared by blade-coating technology,it is noted that the Lb L-type active layer has the unique advantages of high light absorption rate,suitable vertical phase separation and better practicability,so that relevant devices have excellent charge transport and extraction properties.A large-area solar module with a geometric fill factor of more than 90%and an area of 11.52 cm² was manufactured via a blade-coating strategy.The PCE of BHJ-type solar module is10.15%.The Lb L blade-coating strategy can significantly reduce the scaling lag of device efficiency,and the best efficiency of the Lb L-type solar module is 11.86%.（4）In spite of the great success of OSCs in terms of device efficiency and stability at the laboratory scale,pressing demand for high-throughput and cost-effective solutions remains unresolved.In this chapter,the Lb L doctor-blade coating approach significantly promoted the high-speed preparation of the photoactive layer,optimized the thickness of the active layer by synergistic balance of solution concentration and coating speed parameters,and maintained excellent device performance at an ultra-rapid linear coating speed of 30.0 m min^-1.Extended research found that this strategy of realizing high-speed device manufacturing can also be applied to non-halogenated solvent and high humidity conditions and has been further verified in other non-fullerene systems and the scalable slot-die coating technique.Moreover,the techno-economic analysis demonstrated that employing high-speed Lb L deposition methods to fabricate photoactive layers has the great potential to bring down module manufacturing minimum sustainable price.（5）All-polymer solar cells（All-PSCs）exhibit excellent photo-,thermal-stability and mechanical properties compared with small molecule acceptor based photovoltaic system.However,the polymer/polymer blend systems still lag far behind polymer/small molecule acceptor counterparts in power conversion efficiencies（PCEs）.In this chapter,we designed a near-infrared polymer acceptor（PY2F-T）and paired with polymer donor PM6 to fabricate all-PSCs,which show a PCE of 15.01%.Afterwards,PYT as the third component was introduced into the PM6:PY2F-T host system.Owing to the complementary absorption,matched energy level and finely-tuned microstructures of the ternary blend,the PCE is improved up to 17.25%and the optimal ternary all-PSCs system realized superior photostability.Based on the special advantages of Lb L-processing technology as mentioned in chapter 2,3,4,we further employed this method to fabricate Lb L-type all-PSCs.The PCE of over 18%could be obtained in the Lb L-type all-PSCs.