Study On Ternary Strategy Regulating Active Layers To Achieve High Performance Polymer Solar Cells

As a new generation of photovoltaic technology with great potential,polymer solar cells have strong competitivenes with their light weight,low cost,and roll-to-roll large-area fabricate.The ternary strategy is an efficient way to enhance the capture of sunlight of the active layer for the three materials with complementary absorption spectra.It could achieve a high power conversion efficiency（PCE）while maintain a simplified processing of the device fabrication.But due to the complex interactions between three different materials of the ternary active layer,the causes of phase separation of the active layer,charge transfer,and energy transfer are not yet clear.In order to solve the above problems,this work systematically investigated the three components of different systems,and explain the working mechanism of the devices.We studied three ternary systems with the materials selection,devices performance,device physics,morphology of active layers,photophysics and so on.The relationship between material,device and performance was explored,and it provided a useful reference for designing and optimizing ternary system for achieving high-efficiency polymer solar cells in terms of material selection,active layer micro-morphology control,and D/A ratio.The key results as follows:Firstly,taking the high-mobility donor material as the research object,the effects of the introduction of high-mobility polymer materials on the performance were systematically studied.Introducing the high mobility polymer DPPT-TT into the P3:PC₇₁BM-based system,the PCE was significantly increased from 6.18%to 8.30%.DPPT-TT can effectively broaden the absorption spectrum of the active layer and increase the absorption of photons.Time-Correlated Single Photon Counting（TCSPC）spectroscopy results shown that there was an effective F?rster energy resonance transfer between P3 and DPPT-TT.The morphological characterization combined with the evidence of the surface energy interaction between the materials shown that DPPT-TT and P3 had good compatibility to form an"alloyed"donor.The DFT theoretical calculation successfully explained the reason for the voltage change in the system.Secondly,the comprehensive utilization of the synergistic effect of two different acceptor materials,PC₇₁BM and IT-M,could benefit to achieve high efficient polymer organic solar cells.By adjusting the content of PC₇₁BM,the PCE of the PTBTz-2:IT-M:PC₇₁BM-based ternary solar cells were increased from 10.39%to the optimized 12.28%,with V_OC 0.928 V,J_SC 18.70 mA/cm² and FF 70.78%.The ternary system was deeply investigated in terms of device performance,active layer morphology,and exciton dynamics.The concept of synergy unit was proposed through the calculation of state density（DOS）theory.We believe that there is synergy between the two acceptors.Surface energy,morphology analysis,DFT calcultations and femtosecond pumping probes had been employed to investigate the interactions of different component,morphology and the exciton dynamics.The results indicating that the synergistic effect between the two acceptors could promote the morphology of the active layer.And there was a phenomenon of ultrafast energy transfer between the two acceptors.In conclusion,the“synergy unit”acceptors could effectively improve the device performance.Thridly,the photon absorption range of PSCs was greatly expanded through the ternary strategy,and the physicochemical properties of different materials were used to change the morphology of the active layer.By changing the proportion of PC₇₁BM in P2:Y6:PC₇₁BM,with the FF of 74.39%and J_SC of 24.66 mA/cm² were achieved when P2:Y6:PC₇₁BM=1:1.2:0.2,and PCE was achieved at 14.88%finally.The graze-incidence wide-angle X-ray scattering（GIWAXS）was employed to show the molecular packing and orientationthat,after the introduction of PC₇₁BM theπ-πstacking of P2 was intact,and its main carrier transport channel was maintained.The device’s electron mobility was improved by PC₇₁BM with its inherent electron mobility and isotropic characteristics.And the good molecular stacking morphology also shown a good compatibility between P2,Y6 and PC₇₁BM,which was also the nature of the optimal ratio with high FF.Materials can be combined with each other’s superior performance to achieve device performance improvement.