Toluene Processed All-Polymer Solar Cells with 18%Efficiency and Enhanced Stability Enabled by Solid Additive:Comparison Between Sequential-Processing and Blend-Casting

The emergence of polymerized small molecule acceptors(PSMAs)has significantly improved the performance of all-polymer solar cells(all-PSCs).However,the pace of device engineering lacks behind that of materials development,so that a majority of the PSMAs have not fulfilled their potentials.Furthermore,most high-performance all-PSCs rely on the use of chloroform as the processing solvent.For instance,the recent highperformance PSMA,named PJ1-γ,with high LUMO,and HOMO levels,could only achieve a PCE of 16.1%with a high-energy-level donor(JD40)using chloroform.Herein,we present a methodology combining sequential processing(SqP)with the addition of 0.5%wt PC_(71)BM as a solid additive(SA)to achieve an impressive efficiency of 18.0%for all-PSCs processed from toluene,an aromatic hydrocarbon solvent.Compared to the conventional blend-casting(BC)method whose best efficiency(16.7%)could only be achieved using chloroform,the SqP method significantly boosted the device efficiency using toluene as the processing solvent.In addition,the donor we employ is the classic PM6 that has deeper energy levels than JD40,which provides low energy loss for the device.We compare the results with another PSMA(PYF-T-o)with the same method.Finally,an improved photostability of the SqP devices with the incorporation of SA is demonstrated.

Over 18% binary organic solar cells enabled by isomerization of non-fullerene acceptors with alkylthiophene side chains

Side-chain engineering has been demonstrated as an effective method for fine-tuning the optical,electrical,and morphological properties of organic semiconductors toward efficient organic solar cells(OSCs).In this work,three isomeric non-fullerene small molecule acceptors(SMAs),named as BTP-4F-T2C8,BTP-4F-T2EH and BTP-4F-T3EH,with linear and branched alkyl chains substituted on the α or β positions of thiophene as the side chains,were synthesized and systematically investigated.The results demonstrate that the size and substitution position of alkyl side chains can greatly affect the electronic properties,molecular packing as well as crystallinity of the SMAs.After blending with donor polymer D18-Cl,the prominent device performance of 18.25% was achieved by the BTP-4F-T3EH-based solar cells,which is higher than those of the BTP-4F-T2EH-based(17.41%)and BTP-4F-T2C8-based(15.92%)ones.The enhanced performance of the BTP-4F-T3EH-based devices is attributed to its stronger crystallinity,higher electron mobility,suppressed bimolecular recombination,and the appropriate intermolecular interaction with the donor polymer.This work reveals that the side chain isomerization strategy can be a practical way in tuning the molecular packing and blend morphology for improving the performance of organic solar cells.