Study On The Photoelectric Conversion Performance Of New Fused-ring Polymer Acceptors

All-polymer solar cells(all-PSCs)which are composed of p-type polymers and n-type polymers(PD/PA)have received great attention in recent years.Compared with small molecules,the characteristics of polymers give all-PSCs unique advantages,including excellent thermal stability,flexibility,mechanical stability,good film-forming properties and they are more suitable for processing and preparation of large area devices.However,the morphology of the active layer in all-PSCs is difficult to adjust,and the energy conversion efficiency(PCE)of all-polymer solar cells is much lower than polymer solar cells.The main reason of the low PCE in all-PSCs are the low absorption coefficient of n-type polymers and poor electron transport capacity.Therefore,one of the most feasible ways to improve the PCE of all PSCs is to develop new n-type polymers and expand their types to improve the optical absorption coefficient and electronic transport properties of n-type polymers.Recently,introducing fused electron-deficient units into n-type polymers can effectively enhance the light absorption,carrier mobility of n-type polymers and improve the morphology of the active layer.On this basis we designed and synthesized two new polymer acceptors and constructed the all-PSCs by blending them with PM6 and PBDB-T.At the same time,The effect of polymer structure on properties was studied,such as the performance parameters(open circuit voltage Voc;short circuit current Jsc;fill factor FF)and the voltage loss.The main research include:(1)Introducing the DAD fused structure which was commonly used in non-fullerene receptors into the n-type polymer,an acceptor polymer A701 with A'-DAD-A'-D' as the main chain was designed and synthesized.In the A701 polymer,the 1,1-dicyanomethylene-3-indanone(IC),dithienothiophene-[3,2-b]pyrrolobenzothiadiazole(TPBT)and benzodithiophene(BDT)acted as A',DAD and D' units separately.The A701 solution showed a strong absorption peaks at 780 nm,with an absorption coefficient of 6.85×104 cm-1.The LUMO and HOMO energy level of A701 are-3.80 eV and-5.22 eV,and the optical band gap is 1.42 eV.When blending with the classic polymer donor PBDB-T a high VOC of 0.92 V,a Jsc of 18.27 mA cm-2 and an FF of 0.64,and finally a PCE of 10.70%was obtained.The results show that the fused DAD seven-membered ring can not only be used to construct non-fullerene small molecule receptors,but also can be used to construct high-efficiency polymer receptor.(2)In the second work,we further modified the DAD fused ring structure,using benzotriazole(BTA)as the A unit in the seven-membered fused ring DAD,dithienothiophene-[3,2-b]-Pyrrolobenzotriazole(TPBTA)as the DAD unit,and finally a new type of A'-DAD-A'-D' polymer acceptor A702 was designed and synthesized.Compared with A701,1,1-dicyanomethylene-3-indanone(IC)was still selected as the A'unit,while the common electron donor thiophene(T)acted as D'unit.The PCE of the all-polymer solar cell based on PBDB-T:A702 reached 11.84%,of which VOC was 0.90 V,Jsc was 21.93 mA cm-2,FF was 0.60,and voltage loss was 0.55 eV.This work shows that the electron-deficient unit BTA lowers the LUMO energy level of the n-type polymer and reduces the VOC,comparing with the BT unit.At the same time,A702 and PBDB-T formed a better phase separation morphology,and Jsc has been greatly improved.Therefore,changing the DAD unit in the A'-DAD-A'-D' polymer receptor is very important to improve the phase separation morphology of the active layer.