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Two new wide-bandgap polymers (PBDTBDD-Ph and PBDTBDD-PhPh) with different aggregation degrees and fused-ring electron acceptors (FREAs) (ITIC-4T, ITIC-3T and ITIC-2T) with different sizes were synthesized. The work was used to understand how to design the donor polymers and fused-ring electron acceptors (FREAs) for high-performance non-fullerene polymer solar cells (NF-PSCs). The results clearly demonstrated that weakly aggregated donor polymers and small-sized FREAs in appropriate degrees can match well with each other to achieve high power conversion efficiencies (PCEs). In other words, small-sized FREAs can be embedded more easily into the interspace of polymer chains and weakly aggregated polymers can offer larger space for the intercalation of FREAs. As a result, an NF-PSC device based on weakly aggregated polymer PBDTBDD-Ph and small-sized ITIC-3T yielded over 11% PCE. Thus, it would offer a feasible guideline to design high-performance NF-PSCs that meet the requirement of future industry-scale production. [ABSTRACT FROM AUTHOR]

Almost all high-performance non-fullerene polymer solar cells (NF-PSCs) require the optimization of the morphologies of active layers using additional complicated treatments, such as solvent additive processing and thermal annealing. There are still no guidelines currently available regarding controlling the morphologies of polymer donor and fused-ring acceptor blends from a structural point of view to avoid additional post-treatments. Here, we propose an efficient strategy to design polymers that can generate preferred morphologies and then be used to fabricate as-cast high-performance NF-PSCs. New asymmetric benzodithiophene (BDT) building blocks are employed to construct these polymers. The thienylthiol group with a long alkyl chain as one side substituent on BDT can modulate energy levels, broaden absorption spectra and improve solubility. For the key other side chain, bare rigid aryl rings (benzene, naphthalene and biphenyl) are used as lever arms to stir well the elongated acceptor (ITIC) phase and weaken entanglements among polymer chains during the spin-coating process, which enables favorable morphologies without any post-treatments. Finally, the polymer PBDTTAZ-NaPh yielded a power conversion efficiency (PCE) of 11.56%, which is a rare high value for as-cast NF-PSCs. Thus, it would be feasible to employ this proposed strategy to design high-performance NF-PSCs without post-treatment that meet the requirements for future industry-scale production. [ABSTRACT FROM AUTHOR]

An alkyl thiophene unit was employed for the first time as a side chain substituent on an asymmetric benzodithiophene (BDT) building block in the design of novel light-harvesting polymers. A new D–A type polymer (PBDTTh–DTffBT) based on alkylthienyl asymmetric BDT and the well-known 4,7-di(thiophen-2-ethylhexyl)-5,6-difluoro-2,1,3-benzothiadiazole (DTffBT) was synthesized through a palladium catalyzed Stille coupling reaction. Efficient bulk heterojunction solar cells were fabricated by blending PBDTTh–DTffBT with PC71BM. The optimized PBDTTh–DTffBT-based photovoltaic device exhibits an open circuit voltage (VOC) of 0.87 V, a short-circuit current density (JSC) of 15.06 mA cm−2, a fill factor (FF) of 70.4% and a high power conversion efficiency (PCE) of 9.22%. The PCE was higher than the polymers which have the same backbone structure but also have the 1D or 2D symmetric BDT unit. In addition, a PCE of 7.83% with a VOC of 0.91 V, a JSC of 13.62 mA cm−2, and an FF of 63.2% was obtained for PBDTTh–DTffBT/ITIC, which is also impressive for non-fullerene PSCs. The results indicate that our design strategy of introducing an alkylthienyl unit as side chain to fabricate asymmetric BDT-based polymer is efficient in improving the photovoltaic performance. [ABSTRACT FROM AUTHOR]

Bare naphthalene units bonded via the α- and β-positions as side chain substituents on an asymmetric benzodithiophene (BDT) building block were employed in the design of new light-harvesting polymers for the first time. Accordingly, two D–A type polymers, based on naphthyl-substituted BDT as a D-building block and the well-known 4,7-di(thiophen-2-ethylhexyl)-5,6-difluoro-2,1,3-benzothiadiazole (DTffBT) as an acceptor unit, were synthesized. The polymer PBDTβNPFBT with naphthalene bonded via the β-position exhibits an appropriate π–π distance. The naphthalene rings efficiently broaden the absorption and narrow the optical band gap (Eoptg), by extending the degree of π-conjugation, which is beneficial for capturing more photons and thus improving the short-circuit current density (JSC). Meanwhile, PBDTβNPFBT-based devices also exhibit a desirable high open circuit voltage (VOC), due to the low saturation dark current density (JS) arising from the exactly appropriate π–π distance. As a result, the power conversion efficiency (PCE) of 9.80% for the PBDTβNPFBT/PC71BM-based PSC is the highest efficiency ever obtained among the reported BDT and DTBT backbone photovoltaic polymers. In addition, a PCE of 7.33% was obtained for PBDTβNPFBT/ITIC without any treatment, which is also impressive for non-fullerene PSCs. Thus, it can be concluded that a naphthyl unit bonded via the β-position can lead to a better trade-off between Eoptg and VOC, ultimately increasing the PCE dramatically. [ABSTRACT FROM AUTHOR]

A new ultramicroporous conjugated network, P-TCzTAT, enriched with propeller-like carbazole building blocks was designed and synthesized by FeCl3 oxidative coupling polymerization at room temperature. The adsorption isotherm of N2 reveals that the polymer features a high Brunauer–Emmett–Teller (BET) specific surface area of 1028 m2 g−1 and a predominantly narrow pore width of 0.54 nm. The ultramicroporous polymer has strong affinity for CO2, with high sorption abilities of 18.15% at 273 K and 1.1 bar and 10.69% at 273 K/1.1 bar and 298 K/1.1 bar, which can be ascribed to not only its optimal fraction of ultramicropores but also its high nitrogen content derived from the carbazole components. P-TCzTAT also exhibited potential application in gas storage and in CO2/CH4 and CO2/N2 gas separation. [ABSTRACT FROM AUTHOR]