Fabrication Of High Performance Organic Solar Cells By Optimization Morphology With Ternary Strategy

Among many solar cells,organic solar cells have the advantages of designable structure,simple and flexible device preparation process,selective absorption spectrum and enabling to process on flexible or non flexible substrates.Therefore,they have become one of the most attractive research fields in the world.Active layer is the most important part to realize photoelectric conversion.How to design and synthesize high-performance photovoltaic materials?How to optimize the morphology of active layer?These two aspects of improving photoelectric conversion efficiency have always been the research focus in the field of organic solar cells.In this paper,the ternary optimization strategy is adopted to improve the performance of organic solar cell from two dimensions of device fabrication and material design.The main research results are as follows:(1)Based on PM6:L8-BO binary system,a novel non fullerene small molecule acceptor BTA-3BO was introduced to construct an efficient ternary organic solar cell,and the effect of the third component on morphology was systematically studied.The results show that BTA-3BO can enhance the crystallinity,improve carrier mobility,and optimize the charge transfer performance of device.At the same time,the addition of BTA-3BO can improve the morphology of active layer and realize the fine regulation of nanofiber structure.Besides,the addition of BTA-3BO makes up for the lack of absorption in long wavelength direction of binary system,and thus widens the absorption range of active layer.Therefore,the ternary organic solar cell obtains higher exciton dissociation and charge transfer efficiencies,and the degree of charge recombination is greatly reduced.Finally,Jsc increased from 25.9 mA cm-2 to 27.4 mA cm-2,and thus PCE increased from 17.8%to 18.8%.(2)Based on the polymer acceptor PYT,a series of new polymer acceptors PYT-EHx were synthesized by ternary copolymerization strategy,which copolymerized tow small molecule acceptor units(Y5-OD-Br and Y5-EH-Br)with thiophene.The results show that the introduction of short alkyl chain units can enhance the crystallinity of material,obtain closer packing,and thus optimize the charge transfer performance of device.With the increase of the proportion of short alkyl chain units,the crystallinity of material shows a trend of gradient enhancement,and thus PYT-EHx showed enhanced and red shifted absorption.When x>0.2,the "edge on" orientation increases,which has an adverse impact on the charge transfer.The system based on PBDB-T:PYT-EH0.2 achieves the highest and balanced carrier mobility.At the same time,the introduction of short alkyl chain units can optimize the compatibility between materials,and changes regularly with the increase of the proportion of short alkyl chain units.Among them,PYT-EH0.2 has the best compatibility with PBDB-T(χ=0.08 K).Besides,the system based on PBDB-T:PYT-EH0.2 obtains the most appropriate degree of phase separation,which not only has the highest exciton dissociation efficiency and charge transfer efficiency,but also has the weakest degree of charge recombination.Compared to PBDB-T:PYT system,the Jsc based on PBDB-T:PYTEH0.2 system increased from 21.4 mA cm-2 to 22.6 mA cm-2,and FF increased from 67.0%to 70.9%.It is worth noting that the introduction of short alkyl chain units reduces Eloss.without changing the energy level,and thus VOC increased from 0.890 V to 0.920 V.Therefore,the all-PSCs based on PBDB-T:PYT-EH0.2 system obtain the highest efficiency of 14.8%.