Optimizing polymer aggregation and blend morphology for boosting the photovoltaic performance of polymer solar cells via a random terpolymerization strategy

Compared to regular conjugated polymers,the random conjugated terpolymers are usually not beneficial to achieve highly efficient non-fullerene(NF)-based polymer solar cells(PSCs)due to their disordered chemical structures.In this work,we report two random terpolymer donors(PBNB80 and PBNB50)by tuning the molar ratio of electron-accepting units of 1,3-di(thiophen-2-yl)naphtho[2,3-c]thiophene-4,9-dione(NTD)and 1,3-bis(4-chlorothiophen-2-yl)-4 H,8 H-benzo[1,2-c:4,5-c’]dithiophene-4,8-dione(ClBDD),at the same time,the parent polymers(PBNB100 and PBNB00)are also compared to study.These four polymer donors exhibit similar optical bandgaps and gradually deepen highest occupied molecular orbital levels.Importantly,aggregation and self-organization properties of the random terpolymer donors are optimized,which result in the better morphology and crystal coherence length after blending with NF acceptor of BO-4 Cl.Particularly,a PBNB80:BO-4 Cl blend forms an optimal nanoscale phase-separation morphology,thereby producing an outstanding power conversion efficiency of 16.0%,which is much higher than those(12.8%and 10.7%)of their parent binary polymer donor-based devices.This work demonstrates that rational using terpolymerization strategy to prepare random terpolymer is a very important method to achieve highly efficient NF-PSCs.

Efficient Small-Molecule Organic Solar Cells by Modulating Fluorine Substitution Position of Donor Material

Comprehensive Summary The fluorine substitution position in organic semiconductors is critical in improving device performance for organic solar cells(OSCs).Herein,two similar small-molecule donors,B3T-PoF and B3T-PmF,are designed and synthesized,which only differ on the fluorine substitution position on the pendent benzene unit.Although both small-molecule donors exhibit similar absorption profiles and molecular energy levels,B3T-PmF has stronger crystallinity and lower energetic disorder than B3T-PoF.After blending with the non-fullerene acceptor of BO-4Cl,B3T-PmF shows better phase separation and more ordered molecular packing in blend film.As a result,the B3T-PoF:BO-4Cl-based OSC shows a power conversion efficiency(PCE)of 12.3%.In contrast,the B3T-PmF:BO-4Cl-based cell demonstrates obviously increased JSC and FF values,thus yielding an excellent PCE of 14.7%.This study indicates that reasonable selection of fluorine atom substitution position in conjugated side chains is one of the promising strategies for achieving high-performance SM-DSCs.

Modulation of terminal alkyl chain length enables over 15% efficiency in small-molecule organic solar cells

In small-molecule organic solar cells(SM-OSCs),it remains a big challenge to obtain favorable bulk heterojunction morphology by donor material design.Herein,we design and synthesize three small-molecule donors BPF3T-C4,BPF3T-C6 and BPF3T-C8,with different terminal alkyl chains.Although they possess similar absorption profiles and molecular energy levels,their crystallinity gradually decreases with the chain length of the terminal alkyl chains.After blending with an electron acceptor of BO-4Cl,the crystallinity is suppressed and the packing orientations of these donors changed from edge-on to face-on.Simultaneously,the crystallinity of BO-4Cl is gradually weakened with the chain length of the terminal alkyl chain of donor materials.Finally,The BPF3T-C6 with moderate crystallinity exhibits the best phase-separation morphology among these blend films.As a result,the BPF3T-C6:BO-4Cl-based SM-OSC shows an impressive power conversion efficiency of 15.1%.