A 3,3 ′‐Difluoro‐2,2′‐Bithiophene Based Donor Polymer Realizing High Efficiency ( > 17%) Single Junction Binary Organic Solar Cells

In this study, two novel donor –acceptor (D–A) copolymers are designed and synthesized,DTBT-2T andDTBT-2T2F with 2,2 ′-bithiophene or 3,3′-difluoro-2,2′-bithiophene as the donor unit and dithienobenzothiadiazole as the acceptor unit, and used them as donor materials in non-fullerene organic solar cells (OSCs). Due to enhanced planarity of polymer chains resulted by the intramolecular F···S noncovalent int eractions, the incorporation of 3,3′-difluoro-2,2′-bithiophene unit instead of 2,2′-bithiophene into the polymers can enhance their molecular packing, crystallinity and hole mobility. TheDTBT-2T:L8-BO based binary OSCs deliver a power conversion efficiency (PCE) of only 9.71% with aVoc of 0.78  V, aJsc of 20.69  mA cm−2, and anFF of 59.67%. Moreover, the introduction of fluoro atoms can lower the highest occupied molecular orbital levels. As a result,DTBT-2T2F:L8-BO based single-junction binary OSCs exhibited less recombination loss, more balanced charge mobility, and more favorable morphology, resulting in an impressive PCE of 17.03% with a higherVoc of 0.89  V, aJsc of 25.40  mA cm−2, and anFF of 75.74%. These results indicate that 3,3 ′-difluoro-2,2′-bithiophene unit can be used as an effective building block to synthesize high performance polymer donor materials. This work greatly expands the selection range of donor units for constructing high-performance polymers.
Source: Small - Category: Nanotechnology Authors: Tags: Research Article Source Type: research