Design And Photovoltaics Performance Study Of Environmentally Friendly High Efficiency All-polymer Solar Cells

As a new type of solar cells,organic solar cells exibit great potential application value in the fields of information and energy,and open up a new way to fabricate low-cost and high-performance solar cells,mainly due to their advantages of large material selection,strong molecular structure tailorability,good processability,easy"roll-to-roll"continuous printing,and environmental friendliness.Among so far developed organic solar cells,all-polymer solar cells(APSCs)that composed of both polymer donor and polymer acceptor in the active layer,are considered to have great potential in future application due to their excellent thermal and mechanical stability.However,APSCs have faced many hinders such as low charge mobility and undesirable morphology in the active layer,inducing their power conversion efficiency(PCE)significantly lower than that of non-fullerene small molecule solar cells.Based on the aboved fact,this paper explored a series of advanced device processing methods to boost the PCE of APSCs that using N2200 as polymer acceptor,including exploring different strategies of ternary blending,developing new environmentally friendly solvents,regulating the number molecular weight of polymer donors and employing green solvent additives.To realize environmentally friendly solvent processing,a small amount of polyethylene glycol is reasonably grafted onto the side chain of the copolymer.The resulting new wide-bandgap copolymer PBTA-PEG-2%can be easily dissolved in the environmentally friendly solvent 2-methyltetrahydrofuran(2-Me THF).The PBTA-PEG-2%:N2200 binary device processed by 2-Me THF obtained a PCE of 5.98%.PTB7-Th,a narrow band gap copolymer with moderate crystallinity,was introduced into the binary system to compensate for the short board of the absorption profile in the PBTA-PEG-2%:N2200 blend film.Therefore,the short circuit current density(J_SC)of the device is significantly improved,and the PCE reached an unprecedented value of over 9%for the first time.To further improve the PCE of APSCs,PNTB,a narrow band gap copolymer with stronger crystallinity,is incorporated into the PBTA-BO:N2200 binary system to compensate for the short board of the absorption profile in the PBTA-BO:N2200 blend film.F(?)rster resonance energy transfer from PBTA-BO to PNTB occurred,and the phase separation scale of the ternary blend film is reduced,and the?-?stacking of the ternary blend film is tighter.Therefore,the J_SC of the device is significantly improved,and the PCE reached an unprecedented value of over 10%for the first time.To boost the the fill factor(FF)of APSCs,PBTA-BO,a wide band gap copolymer with high hole mobility,is incorporated into the PTzBI:N2200 binary system to construct F(?)rster resonance energy transfer from PBTA-BO to PTzBI.Moreover,the PBTA-BO phase can be embedded into the PTzBI phase and mixed well with PTzBI to form an alloy-like mixed phase.Therefore,the PCE of the device is increased from 9%to 10.12%,and the FF is significantly increased from 68%to 78.33%.To our knowledge,this is the first time that the FF of ternary blended APSCs has achieved more than 78%.In view of the great advantages of environmentally friendly solvents,a new higher boiling point cyclopentyl methyl ether(CPME)was innovatively employed to process PTzBI-Si:N2200 blend film.Compared with PTzBI-Si:N2200 blend film processed by2-Me THF and tetrahydrofuran(THF),PTzBI-Si:N2200 blend film processed by CPME induced higher carrier mobility,tighter?-?stacking,enhanced crystal size and smaller phase separation scale,so the PCE of the device reached an unprecedented value of 11.0%for the first time.On the basis of CPME processing,the effect of the number average molecular weight of PTzBI-Si on device performance and stability based on PTzBI-Si:N2200 was innovatively studied.Compared with the PTzBI-Si:N2200 device based on low M_n PTzBI-Si,the PTzBI-Si:N2200 device based on high M_n PTzBI-Si exhibited significantly improved electron mobility,significantly enhanced crystal size of the N2200 crystal,and smaller phase separation scale of the blend film.Therefore,the device exhibited an unprecedented PCE of11.5%for the first time,as well as better storage and thermal stability.To overcome the challenge that the PCE of APSCs decays rapidly as the thickness of the active layer increases,10%dibenzyl ether(DBE)was introduced into CPME to process PTzBI-Si:N2200 blend film.Due to the higher and thickness-tolerant carrier mobility,tighter?-?stacking,enhanced crystal size and smaller phase separation scale of the blend film,the PCE of the PTzBI-Si:N2200 device is highly tolerant to the thickness of the active layer,and reached an unprecedented value of 9.0%at the thickness of 520 nm.