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Developing high-performance and mechanically robust polymer solar cells (PSCs) is crucial for realizing wearable power sources. While efficient all-polymer solar cells (all-PSCs) can be fabricated from polymerized small-molecule acceptors (PSMAs) with high optical absorption and electron mobilities, they still show limited mechanical robustness. Here, we achieve highly efficient and mechanically robust all-PSCs by designing a PSMA (PYFS-Reg) containing sequence-regular flexible spacers (FSs). The regular incorporation of the FS units into PSMAs is essential in simultaneously improving the electrical and mechanical properties of blend films. As a result, all-PSCs featuring PYFS-Reg achieve a high power conversion efficiency (PCE = 16.1%) and stretchability (crack onset strain (COS) = 22.4%), outperforming PSMAs without FSs (i.e., PYBDT, PCE = 12.6% and COS = 11.7%) or with randomly distributed FSs (i.e., PYFS-Ran, PCE = 12.2% and COS = 18.1%). Importantly, these all-PSCs are fabricated by an environmentally benign, non-halogenated solvent process. To further demonstrate their feasible applications in wearable devices, we construct intrinsically stretchable (IS) all-PSCs by using PYFS-Reg-based active layers, which exhibit a high PCE (10.6%) and excellent device stretchability (strain at PCE80% = 36.7%).

All-polymer solar cells (all-PSCs) are a highly attractive class of photovoltaics for wearable and portable electronics due to their excellent morphological and mechanical stabilities. Recently, new types of polymer acceptors (PAs) consisting of non-fullerene small molecule acceptors (NFSMAs) with strong light absorption have been proposed to enhance the power conversion efficiency (PCE) of all-PSCs. However, polymerization of NFSMAs often reduces entropy of mixing in PSC blends and prevents the formation of intermixed blend domains required for efficient charge generation and morphological stability. One approach to increase compatibility in these systems is to design PAs that contain the same building blocks as their polymer donor (PD) counterparts. Here, a series of NFSMA-based PAs [P(BDT2BOY5-X), (X = H, F, Cl)] are reported, by copolymerizing NFSMA (Y5-2BO) with benzodithiophene (BDT), a common donating unit in high-performance PDs such as PBDB-T. All-PSC blends composed of PBDB-T PD and P(BDT2BOY5-X) PA show enhanced molecular compatibility, resulting in excellent morphological and electronic properties. Specifically, PBDB-T:P(BDT2BOY5-Cl) all-PSC has a PCE of 11.12%, which is significantly higher than previous PBDB-T:Y5-2BO (7.02%) and PBDB-T:P(NDI2OD-T2) (6.00%) PSCs. Additionally, the increased compatibility of these all-PSCs greatly improves their thermal stability and mechanical robustness. For example, the crack onset strain (COS) and toughness of the PBDB-T:P(BDT2BOY5-Cl) blend are 15.9% and 3.24 MJ m–3, respectively, in comparison to the PBDB-T:Y5-2BO blends at 2.21% and 0.32 MJ m–3.

Up‐conversion of triplet into singlet exciton in the emitting layer is believed to be one of the ways that thermally activated delayed fluorescent (TADF) materials may employ to reduce triplet exciton density hence preventing device quenching by triplet excitons. Yet, two donor‐acceptor type molecules; 5‐(4‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)phenyl)‐12‐(3‐(triphenylsilyl) phenyl)‐5,12‐dihydroindolo[3,2‐a]carbazole (SiPhCzTrz) and 5‐phenyl‐12‐(4‐(4‐phenyl‐6‐(3‐(triphenylsilyl) phenyl)‐1,3,5‐triazin‐2‐yl)pheny‐l)‐5,12‐dihydroindolo [3,2‐a]carbazole (SiTrzPhCz), which exhibited different TADF properties depending on the relative positions of their electron donor unit (PhCz) and electron acceptor unit (Trz), show opposite behaviors. These materials are used as sensitizer in phosphorescent solution‐processed organic light emitting diodes (s‐OLEDs) showing moderately high current efficiencies of 19.3 and 20 cd/A, respectively. SiTrzPhCz exhibits stronger TADF properties compared to SiPhCzTrz; however, these stronger TADF characteristics lead to a more pronounced efficiency roll‐off, mainly due to the longer residence time of excitons in SiTrzPhCz, leading to exciton quenching. In contrast, due to their twisted structures, the efficiency roll‐off is efficiently suppressed, particularly for SiTrzPhCz, when both materials are used as hosts. Their twisted structures promote aggregate‐induced emission and prevent aggregation‐caused quenching. Further analysis of exciton dynamics reveals faster decay rate for both singlet and triplet densities in SiPhCzTrz compared to SiTrzPhCz, indicated by its higher fast prompt emission, kFRET and knrT. [ABSTRACT FROM AUTHOR]

Two non‐fullerene acceptors (NFAs), DTBDT‐ICN and DTBDT‐SEH, based on dithienobenzodithiophene (DTBDT) and a 2‐(3‐oxo‐2,3‐dihydroinden‐1‐ylidene) malononitrile (IC) with different side chains of alkylthienyl and alkylthio‐thienyl, respectively, were designed and used as electron acceptors in organic solar cells (OSCs). Both NFAs provide suitable energy level configurations that ensure efficient charge transfer with the donor polymer PBDB‐T, as confirmed by significant photoluminescence reduction in the blend films. However, due to the high planarity together with strong π‐π stacking interactions, the DTBDT‐ICN presented significant aggregation and phase separation in the blend films, leading to suboptimal charge generation. In addition, grazing incidence wide‐angle x‐ray scattering measurements revealed a predominance of edge‐on molecular orientations, which are unfavorable for vertical charge transport. On the other hand, DTBDT‐SEH exhibited less pronounced molecular aggregation and edge‐on orientation properties compared to DTBDT‐ICN, resulting in improved carrier mobility (μe of 3.86 × 10−6 compared to 7.59 × 10−7) and mitigated recombination losses (1.19 kT/q compared to 1.21 kT/q) in OSC devices. The improved morphological features of PBDB‐T:DTBDT‐SEH led to a high power conversion efficiency of 3.31%, which is three times higher than that of PBDB‐T:DTBDT‐ICN‐based devices (1.55%). Furthermore, paired with the high performance polymer PM6, PM6:DTBDT‐SEH demonstrated an enhanced efficiency, reaching 7.03%. [ABSTRACT FROM AUTHOR]

Organic photovoltaics (OPVs) have great potential to drive low‐power consumption electronic devices under indoor light due to their highly tunable optoelectronic properties. Thick devices (>300 nm photo‐active junctions) are desirable to maximize photocurrent and to manufacture large‐scale modules via solution‐processing. However, thick devices usually suffer from severe charge recombination, deteriorating device performances. Herein, the study demonstrates excellent thickness tolerance of all‐polymer‐based PVs for efficient and stable indoor applications. Under indoor light, device performance is less dependent on photoactive layer thickness, exhibiting the best maximum power output in thick devices (34.7 µW cm−2 in 320–475 nm devices). Thick devices also exhibit much better photostability compared with thin devices. Such high thickness tolerance of all‐polymer‐based PV devices under indoor operation is attributed to strongly suppressed space‐charge effects, leading to reduced bimolecular recombination losses in thick devices. The unbalanced charge carrier mobilities are identified as the main cause for significant space‐charge effects, which is confirmed by drift‐diffusion simulations. This work suggests that all‐polymer‐based PVs, even with unbalanced mobilities, are highly desirable for thick, efficient, and stable devices for indoor applications. [ABSTRACT FROM AUTHOR]

High power conversion efficiency (PCE) and long‐term stability are prerequisites for commercialization of organic solar cells (OSCs). Herein, two dimer acceptors (DYTVT and DYTCVT) are developed with different properties through linker engineering, and study their effects as alloy‐like acceptors on the photovoltaic performance and photostability of OSCs. These ternary OSCs effectively combine the advantages of both dimer acceptors. DYTVT, characterized by its high backbone planarity, ensures elevated electron mobility and high glass‐transition temperature (Tg), leading to efficient charge transport and enhanced photostability of OSCs. Conversely, DYTCVT, with its significant dipole moment and electrostatic potential, enhances compatibility of the alloy acceptors with donors and refines the blend morphology, facilitating efficient charge generation in OSCs. Consequently, D18:DYTVT:DYTCVT OSCs exhibit higher PCE (18.4%) compared to D18:MYT (monomer acceptor, PCE = 16.5%), D18:DYTVT (PCE = 17.4%), and D18:DYTCVT (PCE = 17.0%) OSCs. Furthermore, owing to higher Tg of alloy acceptors (133 °C) than MYT (Tg = 80 °C) and DYTCVT (Tg = 120 °C), D18:DYTVT:DYTCVT OSCs have significantly higher photostability (t80% lifetime = 4250 h under 1‐sun illumination) compared to D18:MYT (t80% lifetime = 40 h) and D18:DYTCVT OSCs (t80% lifetime = 2910 h). [ABSTRACT FROM AUTHOR]

Three novel non‐fullerene acceptors (NFAs) (PhBu‐IDT‐BT‐IC, PhBu‐IDT‐BT‐IC4F and PhBu‐IDT‐BT‐IC4Cl) based on 3,8‐dioctyl‐indaceno[1,2‐b:5,6‐b']dithiophene (IDT) core have been designed and synthesized with and without halogen (F and Cl) substitution. The NFAs showed high thermal stability. The ultraviolet–visible absorption studies in solution and thin film for the three acceptors revealed maximum absorption from 687 to 732 nm and 731 to 847 nm, respectively. The onset of absorption in the thin film was found to be extending up to around 960 nm for PhBu‐IDT‐BT‐IC4Cl. The optical band gap ranged from 1.30 to 1.41 eV, which are very low and useful for photovoltaic application. The introduction of halogen appreciably altered the LUMO energy levels, whereas the HOMO energy levels were nearly intact. These small molecule non‐fullerene acceptors could be used as potential acceptors in bulk heterojunction organic photovoltaic (BHJ‐OPV) applications. [ABSTRACT FROM AUTHOR]