High Efficiency Organic Solar Cells Processed By Sequential Spin-Coating

In recent years,great progress has been made in the research of organic solar cells(OSCs).The efficiency of the latest single-junction OSCs has exceeded 19%,which further reduces the efficiency gap with the traditional crystalline silicon solar cells.However,at present,the efficiency and stability of OSCs are far from meeting the requirements of practical applications.Efficient synthesis of active layer materials and optimization of device structure are also needed.For BHJ devices,it is inevitable that some acceptor materials are connected with the wrong electrode,or some materials are not connected with the positive electrode or the negative electrode,forming an isolated phase.These two conditions are extremely unfavorable to improve the efficiency of OSCs.In contrast,in the layer-by-layer(LBL)device prepared by continuous spin coating method,the donor layer and acceptor layer are prepared separately,so that the donor material is connected with the anode and the acceptor material is connected with the cathode,avoiding the formation of the above isolated phase.The LBL-type device structure is a potential means to improve the performance of OSCs.In this paper,we use sequential spin coating method to prepare LBL devices.By accurately regulating the morphology of donor layer and acceptor layer,we can realize the preparation of efficient pseudo bilayer planar heterojunction organic solar cells.(1)Using two polymer acceptors P1 and P2 synthesis by the subject,it is found that P2 has better photovoltaic performance through a series of optimization.,so P2 is selected to prepare LBL device.In contrast,the performance parameters of LBL device are better than BHJ device.Through the corresponding characterization,it is found that the improvement of device performance is due to less bimolecular recombination and more balanced carrier mobility in LBL devices.Our research shows that the efficiency of LBL devices prepared by sequential spin coating is better than that of conventional BHJ devices by selecting appropriate materials and optimization methods.(2)In the polymer/small molecule system based on PBDB-T:Py-Cl,BHJ devices and LBL devices were prepared respectively.Among them,the PCE of BHJ device is9.48%,and that of LBL device is 9.63%.The PCE of LBL device is obviously better than that of BHJ device.Compared with BHJ devices,the improvement of PCE is attributed to the improvement of Fill Factor,which is obviously determined by less bimolecular recombination and more balanced carrier mobility in LBL devices.(3)We introduced a newly small molecule acceptor TIT-2Cl as the three components into the PM6:Y6 system,obtained a high PCE of 17.00%.The PCE of LBL ternary OSCs is still better than that of BHJ ternary OSCs.The efficiency of LBL ternary OSCs reached 18.18%.We have deeply explored the reasons for the efficiency difference,and found that the efficiency improvement is mainly due to the formation of vertical phase distribution in LBL devices and the improvement of carrier transmission capacity.The research shows that by selecting the appropriate third component material and adopting LBL device structure,some problems existing in BHJ devices can be avoided,so as to further improve the efficiency of OSCs.