Post-sulphuration enhances the performance of a lactone polymer donor

Remarkable progress has been made in conjugated copoly-mer donors due to the development of novel fused-ring ac-ceptor(FRA)building units[1−15].The copolymers based on FRA units have delivered excellent power conversion efficien-cies(PCEs)up to 18.69%in organic solar cells(OSCs)[16].Fused-ring aromatic lactones are promising FRA units[17−19].

18% Efficiency organic solar cells

In 1995,Yu et al.[1]first reported bulk-heterojunction(BHJ)solar cells with a conjugated polymer donor and a fullerene acceptor as the active materials.From then on,BHJ organic solar cells(OSCs)have attracted academic and industrial interests due to the advantages like lightweight,flexibility and roll-to-roll fabrication.Nowadays,17%power conversion efficiencies(PCEs)have been achieved in the state-of-the-art OSCs[2,3].The remarkable progress in OSCs relies on the continuously emerging new materials and device fabrication technologies,and the understanding on film morphology and device physics[4,5].

Thiolactone copolymer donor gifts organic solar cells a 16.72% efficiency

Since 1995,bulk-heterojunction organic solar cells consisting of one or two organic donors and one or two organic acceptors have been fighting for high power conversion efficiencies(PCEs)and good stability[1].Until recent years,this next-generation photovoltaic technology starts to offer decent PCEs,shedding the light on commercialization,and attracting great attention again[2-14].Compared w让h the continuously emerging highperformance nonfullerene acceptors,high-performance donors are rare.

Fused-ring bislactone building blocks for polymer donors

The past 5 years have witnessed the rapid development of organic solar cells based on nonfullerene acceptors(NFAs)[1-26].The state-of-the-art NFA-based single-junction and tandem solar cells afforded 18.22%(certified 17.6%)and 17.36%(certified 17.29%)power conversion efficiencies(PCEs),respectively[27,28].Wide-bandgap(WBG)polymer donors are ideal partners for NFAs.They present complementary absorption with that of low-bandgap NFAs and deep the highest occupied molecular orbital(HOMO)levels.Therefore,solar cells based on a WBG polymer and a NFA can generate high short-circuit current density(Jsc)and open-circuit voltage(Voc)[29].Meanwhile,some WBG polymers show high crystallinity and mobility,gifting the solar cells high fill factors(FF)[30].Recently,our group first reported efficient WBG D-A copolymer donors based on fused-ring aromatic lactone(FRAL)acceptor units.