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Laboratory-scale all-polymer solar cells (all-PSCs) have exhibited remarkable power conversion efficiencies (PCEs) exceeding 19%. However, the utilization of hazardous solvents and nonvolatile liquid additives poses challenges for eco-friendly commercialization, resulting in the trade-off between device efficiency and operation stability. Herein, an innovative approach based on isomerized solid additive engineering is proposed, employing volatile dithienothiophene (DTT) isomers to modulate intermolecular interactions and facilitate molecular stacking within the photoactive layers. Through elucidating the underlying principles of the DTT-induced polymer assembly on molecular level, a PCE of 18.72% is achieved for devices processed with environmentally benign solvents, ranking it among the highest record values for eco-friendly all-PSCs. Significantly, such superiorities of the DTT-isomerized strategy afford excellent compatibility with large-area blade-coating techniques, offering a promising pathway for industrial-scale manufacturing of all-PSCs. Moreover, these devices demonstrate enhanced thermal stability with a promising extrapolated T80 lifetime of 14 000 h, further bolstering their potential for sustainable technological advancement. The isomerized solid additive engineering based on volatile dithienothiophene (DTT) isomers is empolyed to achieve a remarkable PCE of 18.72% for all-PSCs processed with green solvent. More importantly, the all-PSCs fabricated with this approach offer excellent compatibility with large-area blade-coating techniques, and demonstrate exceptional thermal stability with extrapolated T80 lifetime of 14 000 h.image

Organic photovoltaics (OPVs) are one of the most promising technologies to power indoor electronic devices. However, the limited types and design strategies of medium band-gap acceptor materials hinder the development of indoor OPVs. Currently, the state-of-the-art non-fullerene acceptors (NFAs) are Y6 and its derivatives, which are based on an A–DA′D–A structure. In this paper, we report the modification of the Y6 structure by replacing Y6's D unit (thieno[3,2-b]thiophene) with benzothiophene, and synthesize two novel NFAs (LBT-DF and LBT-SCl) for indoor applications. The use of the benzothiophene unit reduces the intermolecular charge transfer effect, thus blue-shifting the absorption spectra and up-shifting the LUMO energy levels of the NFAs. As a result, LBT-SCl achieves a higher Voc and thus PCE (up to 25.1%) than Y6 (22.2%) under indoor conditions. Interestingly, these two NFAs exhibit a non-planar aromatic structure, which is rarely observed in the published NFAs, because a better coplanar molecular configuration is usually considered as the critical factor in realizing high PCE. Different from the above mentioned molecular design concept, we find that non-planar structure acceptors also have great potential in OPVs. Our work provides an effective OPV material design guideline for developing high-performance indoor OPVs and also opens a new direction for the design of NFAs.

In the field of non-fullerene organic solar cells (OSCs), compared to the rapid development of non-fullerene acceptors, the progress of high-performance donor polymers is relatively slow. The property and performance of donor polymers in OSCs are often sensitive to the molecular weight of the polymers. In this study, a chlorinated donor polymer named D18-Cl is reported, which can achieve high performance with a wide range of polymer molecular weight. The devices based on D18-Cl show a higher open-circuit voltage (VOC) due to the slightly deeper energy levels and an outstanding short-circuit current density (JSC) owing to the appropriate long periods of blend films and less ([6,6]-phenyl-C71-butyric acid methyl ester) (PC71BM) in mixed domains, leading to the higher efficiency of 17.97% than those of the D18-based devices (17.21%). Meanwhile, D18-Cl can achieve high efficiencies (17.30–17.97%) when its number-averaged molecular weight (Mn) is ranged from 45 to 72 kDa. In contrast, the D18-based devices only exhibit relatively high efficiencies in a narrow Mn range of ≈70 kDa. Such property and performance make D18-Cl a promising donor polymer for scale-up and low-cost production. © 2021 Wiley-VCH GmbH

High-performance, cost-effective hole-transport materials (HTMs) are greatly desired for the commercialization of perovskite solar cells (PVSCs). Herein, two new HTMs, TPA-FO and TPA-PDO, are devised and synthesized, which have a donor-acceptor-donor (D-A-D) type molecule design featuring carbonyl group-functionalized arenes as the acceptor (A) units. The carbonyl group at the central core of HTMs can not only tune frontier molecular orbital (FMO) energy levels and surface wettability, but also can enable efficient surface passivation effects, resulting in reduced recombination loss. When employed as HTMs in inverted PVSCs without using dopant, TPA-FO with one carbonyl group yields a high power conversion efficiency (PCE) of 20.24%, which is among the highest values reported in the inverted PVSCs with dopant-free HTMs. More importantly, the facile one-step synthetic process enables a low cost of 30 USD g–1 for TPA-FO, much cheaper than the most studied HTMs used for high-efficiency dopant-free PVSCs. These results demonstrate the potential of D-A-D type molecules with carbonyl group-functionalized arene core in developing the low-cost dopant-free HTMs toward highly efficient PVSCs.

Chemical modifications of non-fullerene acceptors (NFAs) play vital roles in the development of high efficiency organic solar cells (OSCs). In this work, on the basis of the previously reported molecule named Y6-1O, chlorination and inner side-chain engineering are adopted to endow the corresponding devices with higher open-circuit voltage (VOC) and short-circuit current density (JSC) as well as good morphology for high fill factor (FF). As a result, the molecule named BTP1O-4Cl-C12 can help achieve a higher power conversion efficiency (PCE) of 17.1% than that of Y6-1O (16.1%). Furthermore, the following comparisons between BTP1O-4Cl-C12 and the two symmetric acceptors named BTP2O-4Cl-C12 and BTP-4Cl-C12 demonstrate the effect of asymmetric alkoxy substitution on the outer side chains, which not only achieves a balance between VOC and JSC, but also help obtain appropriate morphology for efficient charge dissociation and suppressed charge recombination. Therefore, the asymmetric BTP1O-4Cl-C12 can achieve a higher PCE compared to the symmetric BTP2O-4Cl-C12 and BTP-4Cl-C12. The work not only reports an excellent NFA for high-performance OSCs, but also puts forward a series of methods for consecutive chemical modifications on Y-series acceptors, which can be further applied to boost the PCE of OSCs to a higher level. © 2021 Wiley-VCH GmbH

Fluorination of end groups has been a great success in developing efficient small molecule acceptors. However, this strategy has not been applied to the development of polymer acceptors. Here, a dihalogenated end group modified by fluorine and bromine atoms simultaneously, namely IC-FBr, is first developed, then employed to construct a new polymer acceptor (named PYF-T) for all-polymer solar cells (all-PSCs). In comparison with its non-fluorinated counterpart (PY-T), PYF-T exhibits stronger and red-shifted absorption spectra, stronger molecular packing and higher electron mobility. Meanwhile, the fluorination on the end groups down-shifts the energy levels of PYF-T, which matches better with the donor polymer PM6, leading to efficient charge transfer and small voltage loss. As a result, an all-PSC based on PM6:PYF-T yields a higher power conversion efficiency (PCE) of 14.1% than that of PM6:PY-T (11.1%), which is among the highest values for all-PSCs reported to date. This work demonstrates the effectiveness of fluorination of end-groups in designing high-performance polymer acceptors, which paves the way toward developing more efficient and stable all-PSCs. © 2020 Wiley-VCH GmbH

Selecting suitable aromatic rings to develop high‐performance asymmetric small‐molecule acceptors (SMAs) is of great significance. In this work, we designed and successfully synthesized two asymmetric SMAs, namely BTN‐4F and BTSe‐4F, by incorporating pyrrole and selenophene unit into the central cores, respectively. Compared with the selenophene‐fused counterpart BTSe‐4F, BTN‐4F displays slightly upshifted energy levels and red‐shifted absorption spectrum (about 40 nm in film) due to the strong electron‐donating ability of N atoms in pyrrole. When matching with PM6, BTN‐4F‐based device gives a higher power conversion efficiency (PCE) (15.82%) due to the simultaneously enhanced open circuit voltage (VOC), short‐circuit current density (JSC), and fill fator (FF), compared with those of BTSe‐4F‐based device. The higher VOC coincides with the shallower LUMO energy level of BTN‐4F; the enhanced JSC mainly results from the broadened and enhanced absorption; the increased FF could be ascribed to the weaker bimolecular recombination, more balance charge transport and more favorable morphology. It should be mentioned that BTN‐4F‐based device yield a lower energy loss than that of BTSe‐4F‐based device. Overall, our work demonstrates that pyrrole‐fused SMAs shows great potential in realizing low Eloss while yielding high JSC and PCE, which paves a new way to develop high‐performance SMAs.