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.

18.55% Efficiency Polymer Solar Cells Based on a Small Molecule Acceptor with Alkylthienyl Outer Side Chains and a Low-Cost Polymer Donor PTQ10

The development of A-DA′D-A type small molecule acceptors(SMAs)has promoted the rapid progress of polymer solar cells(PSCs)in recent years.The outer side chains on the terminal thiophene ring and inner side chains on nitrogen atoms of the pyrrole ring of the DA′D fused ring play important roles in the photovoltaic performance of the SMAs.Here,we synthesized two new SMAs,2,2′-((2Z,2′Z)-((12,13-bis(2-ethylhexyl)-3,9-bis(4-(2-ethylhexyl)thiophen-2-yl)-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methaneylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile(T2EH)and 2,2′-((2Z,2′Z)-((12,13-bis(2-ethylhexyl)-3,9-bis(3-(2-ethylhexyl)phenyl)-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methaneylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)(P2EH),with 2-ethylhexylβ-substituted thienyl or phenyl as the outer side chains,respectively,to improve the photovoltaic properties of the SMAs.Compared with P2EH,T2EH exhibits closerπ−πstacking,slightly red-shifted absorption,and higher electron mobility.Moreover,the active layer of T2EH blended with the low-cost polymer donor poly[(thiophene)-alt-(6,7-difluoro-2-(2-hexyldecyloxy)quinoxaline)](PTQ10)possesses higher mobilities,a longer lifetime,and less recombination of the charge carriers in comparison with that of the PTQ10:P2EH active layer.Eventually,the PTQ10:T2EH-based PSCs showed an outstanding power conversion efficiency(PCE)of 18.55%,while the PSC based on PTQ10:P2EH displayed a PCE of 17.50%.Importantly,18.55%is the highest PCE in the PTQ10-based binary PSCs so far.The results indicate that T2EH is one of the best SMAs for the PTQ10-based PSCs and is a promising SMA for the application of PSCs.

Two Typical Examples of Scaling Ionic Partition Scheme for Estimating Correlation Energy of A_2 Type Molecules

Based on the calculation results of pair correlation energy contributions of the various electron pairs in Na2 and H2NNH2 systems and the application of the scaling ionic partition scheme for symmetrical A2 type systems, the to-tal correlation energies of Na2 and H2NNH2 have been reproduced by using this simple scheme. The two results show that the absolute deviations are within an acceptable range of error, however, in this way, more than 90% of computational work can be saved. The most attractive result in present paper is that, in these two molecules the co-efficients c1 and c2 in the estimation equation can be obtained by the proportion of correlation energy of A- to that of A+ singlet system. Therefore, it is believed that the proposed ionic partition scheme for symmetrical A2 mole-cules would be very useful to estimate the correlation energies of large symmetrical molecules.

Acceptor-Donor-Acceptor Type Small Molecular Low Band Gap Organic Semiconductors Containing 2-Dicyanomethylen- 3-cya n o-4, 5, 5-t rim ethyl-d i hyd rofu ran

Acceptor-donor-acceptor type compounds WI--W3 were designed and synthesized. These compounds had the same donor moiety of 2,6-di（tbiophen-2-yl）dithieno[3,2-b：2＇,3＇-d]thiophene and different acceptor groups of 2-dicyanomethylen-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran （TCF）, dicyanovinyl （DCV） and 3-ethyl-2-thioxothia- zolidin-4-one. Experimental results showed all compounds had high thermal stability and strong absorption in the visible light region. Among them, compound Wl with TCF as acceptor group displayed the lowest LUMO energy level of-3.74 eV and the smallest HOMO-LUMO band gap of 1.74 eV, suggesting the potential applications of TCF unit in low band gap organic semiconductors.