A non-fullerene acceptor with a high relative dielectric constant (εr) over 9 is developed. It offers an efficiency of 8.5%, which is the best result for organic solar cells employing high εr materials. Further research should focus on morphology optimization to make high εr practically useful in devices.

All-polymer solar cells (all-PSCs) composed of conjugated polymers as both donor and acceptor components in bulk heterojunction photoactive layers have attracted increasing attention. However, it is a big challenge to achieve optimal morphology in polymer:polymer blends. In response, we report herein a new strategy to adjust the nanoscale organization for all-PSCs. Specifically, side chain engineering of the well-known naphthalene diimide (NDI)-based polymer N2200 is modulated by introducing a fraction of linear oligoethylene oxide (OE) side chains to replace branched alkyl chains on the NDI units and by synthesizing a series of NDI-based polymer acceptors NOE x, where x is the percentage of OE chain substituted NDI units relative to total NDI units. Compared to the reference polymer NOE0, OE-chain-containing polymer NOE10 offers a much higher power conversion efficiency (PCE) of 8.1% with a record high fill factor (FF) of 0.75 in all-PSCs. Moreover, the NOE10-based all-PSC exhibits excellent long-term and thermal stabilities with >97% of the initial PCE being maintained after 300 h of aging at 65 °C. This work demonstrates an effective morphology optimization strategy to achieve highly efficient and stable all-PSCs and shows the excellent potential of NOE10 as an alternative to commercially available acceptor polymers N2200.

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A series of internal donor-acceptor type of copolymers containing benzothiadiazole and four thiophene rings (bis(2,2 0 -dithienyl)benzothiadiazole) in their repeating units were synthesized and characterized. The effect of the position of alkyl groups attached to different thiophene rings of the new polymers on their optical, electrochemical, and photovoltaic properties was investigated and compared with poly(2,7-(9,9-dioctylfluorene)-alt-5,5-(4 0 ,7 0 -di-2-thienylbenzo[c][1,2,5]thiadiazole)) (PFO-DBT). One of the new polymers, poly(2,7-(9,9-dioctylfluorene)-alt-5 0 ,5 0 -(4,7-bis(3 0 -hexyl-2,2 0 -bithiophen-5-yl)benzo[c][1,2,5] thiadiazole)) (PFO-M3), showed the best device performance with a power-conversion efficiency of 2.63%, an open-circuit voltage of 0.86 V, a short-circuit current density of 5.86 mA cm -2 and a fill factor of 0.52, which is better as compared with PFO-DBT. This work demonstrated that increasing the number of thiophene rings in the repeating units of the donor-acceptor polymers is a simple and effective method to red-shift their absorption spectra and also improve their solar cell performance.

Nonfullerene acceptors (NFAs) have contributed significantly to the progress of organic solar cells (OSCs). However, most NFAs feature a large fused-ring backbone, which usually requires a tedious multiple-step synthesis, and are not applicable to commercial applications. An alternative strategy is to develop nonfused NFAs, which possess synthetic simplicity and facile tunability in optoelectronic properties and solid-state microstructures. In this work, we report two nonfused NFAs, BTCIC and BTCIC-4Cl, based on an A–D–A′–D–A architecture, which possess the same electron-deficient benzothiadiazole central core but different electron-withdrawing terminal groups. The optical properties, energy levels, and molecular crystallinities were finely tuned by changing the terminal groups. Moreover, a decent power conversion efficiency of 9.3 and 10.5% has been achieved by BTCIC and BTCIC-4Cl, respectively, by blending them with an appropriate polymer donor. These results demonstrate the potential of A–D–A′–D–A type nonfused NFAs for high-performance OSCs. Further development of nonfused NFAs will be very fruitful by employing appropriate building blocks and via side-chain optimizations.

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One of the most important factors that limits the efficiencies of bulk‐heterojunction organic solar cells (OSCs) is the modest open‐circuit voltage (Voc) due to their large voltage loss (Vloss) caused by significant nonradiative recombination loss. To boost the performance of OSCs toward their theoretical limit, developing high‐performance donor: acceptor systems featuring low Vloss with suppressed nonradiative recombination losses (<0.30 V) is desired. Herein, high performance OSCs based on a polymer donor benzodithiophene‐difluorobenzoxadiazole‐2‐decyltetradecyl (BDT‐ffBX‐DT) and perylenediimide‐based acceptors (PDI dimer with spirofluorene linker (SFPDI), PDI4, and PDI6) are reported which offer a high power conversion efficiency (PCE) of 7.5%, 56% external quantum efficiency associated with very high Voc (>1.10 V) and low Vloss (<0.60 V). A high Voc up to 1.23 V is achieved, which is among the highest values reported for OSCs with a PCE beyond 6%, to date. These attractive results are benefit from the suppressed nonradiative recombination voltage loss, which is as low as 0.20 V. This value is the lowest value for OSCs so far and is comparable to high performance crystalline silicon and perovskite solar cells. These results show that OSCs have the potential to achieve comparable Voc and voltage loss as inorganic photovoltaic technologies.