Triazine derivative as volatile solid additive for non‐halogenated solvent and thermal annealing‐free processed organic solar cells with over 18%efficiency

Volatile solid additive(VSA)has been demonstrated to be an effective strategy to optimize the morphology of the active layer for high‐performance organic solar cells(OSCs).Most of the reported OSCs with VSA are processed by chloroform(CF)and relies on thermal annealing(TA)posttreatment.However,the CF solvent problems of low boiling point,toxicity,and environmentalunfriendly as well as increasing cost from TA restricted the large‐scale production.Here,a simple‐structured and low‐cost triazine derivative 2,4,6‐trichloro‐1,3,5‐triazine(TCT)as a VSA was introduced into PM6:BTP‐eC9‐based OSCs.Employing the TCT additive,the nonhalogenated solvent(o‐xylene)processed OSCs without TA treatment and delivered higher power conversion efficiencies(PCEs)in comparison to the TA‐treated counterpart.Benefiting from the intermolecular interactions between TCT and the active layer materials,the TCT‐treated blend films exhibited optimized morphology and enhanced crystallinity.As a result,the PM6:BTP‐eC9 OSCs achieved a champion PCE of 18.18%and fill factor(78.5%),which is among one of the most advanced nonhalogenated solvent‐processed and annealing‐free OSCs.Meanwhile,the TCT‐treated blend films also demonstrated the better photostability compared to the control device.This work provides a guideline of triazine derivatives as VSA for high‐performance OSCs with TA‐free and nonhalogenated solvent‐processing treatment.

Synergetic Alkoxy Side-Chain and Chlorine-Contained End Group Strategy toward High Performance Ultra-Narrow Bandgap Small Molecule Acceptors

Ultra-narrow bandgap(ultra-NBG)small molecule acceptors(SMAs)show great potential in organic solar cells(OSCs)due to the extended near-infrared(NIR)absorption.In this work,a synergetic alkoxy side-chain and chlorine-contained end group strategy is employed to achieve A-DA'D-A type ultra-NBG SMAs by introducing alkoxy chains with oxygen atom at the second position into the thiopheneβposition as well as replacing the F atoms with Cl atoms in the end group.As a result,the heptacyclic BZO-4F shows a redshifted absorption onset(960 nm)compared with Y11(932 nm)without oxygen atoms in the side chains.Then,the fluorinated end groups are substituted with the chlorinated ones to synthesize BZO-4Cl.The absorption onset of BZO-4Cl is further redshifted to 990 nm,corresponding to an optical ultra-NBG of 1.25 eV.When blending with the polymer donor PBDB-T,the binary devices based on PBDB-T:BZO-4F and PBDB-T:BZO-4Cl deliver power conversion efficiencies(PCEs)over 12%.Furthermore,ternary devices with the addition of BZ4F-O-1 into PBDB-T:BZO-4Cl system achieve the optimal PCE of 15.51%.This work proposes a synergetic alkoxy side-chain and chlorine-contained end group strategy to achieve A-DA'D-A type ultra-NBG SMAs,which is important for future molecular design.