Yingzhi Jin

In article number 2100746, Shengzhong (Frank) Liu, Zhong-Shuai Wu and co-workers report an aqueous MXene/PH1000 hybrid ink for inkjet printing of planar micro-supercapacitors, which can serve as a flexible energy storage unit for Si film solar cells and can supply power for printable temperature sensors. Such printable inks are expected to allow for scalable and customizable fabrication of power sources for next-generation, self-sustaining, wearable, and implantable microelectronics.

A new near-infrared polymer acceptor, PY2F-T, was developed by connecting the non-fullerene small-molecule acceptor building block (Y6 derivative) through a thiophene spacer. By using PM6 as the polymer donor and PYT as the third component, we found the ternary all-polymer solar cell (all-PSC) exhibited an impressively high power conversion efficiency of 17.2%, which is much higher than those of the binary all-PSCs (14.4% for PM6:PYT and 15.0% for PM6:PY2F-T). Impressively, the optimal ternary device shows superior light-soaking stability and photo-thermal stability.

Understanding the fundamental origin of morphological degradation in non-fullerene acceptor-based organic solar cells is challenging. In the April 2021 issue of Nature Materials, Ghasemi et al. reveal that the most thermodynamically unstable and low-miscibility systems with high Flory-Huggins interaction parameter (χ) exhibit the most kinetically stable (low diffusion) morphology for superior device operation stability under thermal stress.

The advent of non-fullerene acceptors (NFAs) has enabled organic solar cells to reach power conversion efficiencies that were previously thought unreachable. However, in a recent Nature Materials article, Karuthedath and colleagues show that the electrostatic environment at the interface might put a limit to how much further they can be improved.

1,10-decanediol is introduced as an additive that can improve the crystalline of polymer and protect PM6 film from less erosion during the sequential deposition (SD) process. The strategy is applied to fabricate pseudo-planar heterojunction (PPHJ) organic solar cells with ideal vertical phase separation through SD processing. The champion PPHJ device demonstrates a high efficiency (16.93%) and fill factor (77.45%).

Abstract

Acquiring precision adjustable morphology of the blend films to improve the efficiency of charge separation and collection is a constant goal of organic solar cells (OSCs). Here, the above problem is improved by synergistically combining the sequential deposition (SD) method and the additive general strategy. By adding one additive 1,10-decanediol (DDO) into PM6 and another 1-chloronaphthalene (CN) into Y6, the molecule orientation of PM6 and the crystallite texture of the Y6 all become order. During the SD processing, a vertical phase separation OSCs device is formed where the donor enrichment at the anode and acceptor enrichment at the cathode. In comparison, the SD OSCs device with only CN additive still displays the bulk-heterojunction morphology similar to PM6:Y6 blend film. The morphology with vertical phase distribution can not only inhibit charge recombination but also facilitate charge collection, finally enhancing the fill factor (FF) and photocurrent in binary additives SD-type OSCs. As a result, the binary additives SD-type OSCs with blend film PM6+DDO/Y6+CN exhibit a high FF of 77.45%, enabling a power conversion efficiency as high as 16.93%. This work reveals a simple but effective approach for boosting high-efficiency OSCs with ideal morphologies and demonstrates that the additive is a promising processing alternative.

In this study, a chlorinated polymer named D18-Cl is designed and synthesized, leading to highly efficient (near 18%) organic solar cells, yet whose performance is insensitive to its molecular weight. These advantages make D18-Cl a more promising donor polymer than previously reported polymer D18 for scale-up and low-cost production.

Abstract

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 (V _OC) due to the slightly deeper energy levels and an outstanding short-circuit current density (J _SC) 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 (M _n) is ranged from 45 to 72 kDa. In contrast, the D18-based devices only exhibit relatively high efficiencies in a narrow M _n range of ≈70 kDa. Such property and performance make D18-Cl a promising donor polymer for scale-up and low-cost production.

Selenophene end-capped asymmetric heteroheptacene core is used to construct an efficient nonfullerene acceptor (MQ6) which shows increased carrier transport due to the enhanced O⋅⋅⋅Se intramolecular noncovalent interaction as well as the increased dipole moment. MQ6 exhibits an outstanding efficiency of 16.39 % when blended with a wide band gap copolymer.

Abstract

Nonfullerene acceptors (MQ3, MQ5, MQ6) are synthesized using asymmetric and symmetric ladder-type heteroheptacene cores with selenophene heterocycles. Although MQ3 and MQ5 are constructed with the same number of selenophene heterocycles, the heteroheptacene core of MQ5 is end-capped with selenophene rings while that of MQ3 is flanked with thiophene rings. With the enhanced noncovalent interaction of O⋅⋅⋅Se compared to that of O⋅⋅⋅S, MQ5 shows a bathochromically shifted absorption band and greatly improved carrier transport, leading to a higher power conversion efficiency (PCE) of 15.64 % compared to MQ3, which shows a PCE of 13.51 %. Based on the asymmetric heteroheptacene core, MQ6 shows an improved carrier transport induced by the reduced π–π stacking distance, related with the increased dipole moment in comparison with the nonfullerene acceptors based on symmetric cores. MQ6 exhibits a PCE of 16.39 % with a V _OC of 0.88 V, a FF of 75.66 %, and a J _SC of 24.62 mA cm⁻².

Newly synthesized hexabenzocoronene (HBC)–osmapentalyne complexes that combine fragments of graphene and metalla-aromatics are emerging as cathode interlayer materials. Further extending the d_π –p_π conjugated systems of osmapentalynes, the most successful complex, in this work, HBC-S is found to boost the efficiency of non-fullerene solar cells to over 18%.

Abstract

Interface engineering is a critical method by which to efficiently enhance the photovoltaic performance of nonfullerene solar cells (NFSC). Herein, a series of metal–nanographene-containing large transition metal involving d_π –p_π conjugated systems by way of the addition reactions of osmapentalynes and p-diethynyl-hexabenzocoronenes is reported. Conjugated extensions are engineered to optimize the π-conjugation of these metal–nanographene molecules, which serve as alcohol-soluble cathode interlayer (CIL) materials. Upon extension of the π-conjugation, the power conversion efficiency (PCE) of PM6:BTP-eC9-based NFSCs increases from 16% to over 18%, giving the highest recorded PCE. It is deduced by X-ray crystallographic analysis, interfacial contact methods, morphology characterization, and carrier dynamics that modification of hexabenzocoronenes-styryl can effectively improve the short-circuit current density (J _sc) and fill factor of organic solar cells (OSCs), mainly due to the strong and ordered charge transfer, more matching energy level alignments, better interfacial contacts between the active layer and the electrodes, and regulated morphology. Consequently, the carrier transport is largely facilitated, and the carrier recombination is simultaneously impeded. These new CIL materials are broadly able to enhance the photovoltaic properties of OSCs in other systems, which provides a promising potential to serve as CILs for higher-quality OSCs.

Nature Energy, Published online: 07 June 2021; doi:10.1038/s41560-021-00843-4

Organic solar cells based on non-fullerene acceptors have enabled high efficiencies yet their charge dynamics and its impact on the photovoltaic parameters are not fully understood. Now, Chen et al. provide a general description of non-radiative voltage losses in both fullerene and non-fullerene solar cells.

Polydopamine, a melanin analogue, is an excellent trap for alkylperoxyl radicals (ROO^., typically formed during autoxidation of lipid substrates) only in the presence of hydroperoxyl radicals (HOO^.). Activation of the ortho-quinone moieties by HOO^., and formation of exposed semiquinones are proposed as the reason of the peculiar antioxidant activity.

Abstract

Melanins are stable and non-toxic biomaterials with a great potential as chemopreventive agents for diseases connected with oxidative stress, but the mechanism of their antioxidant action is unclear. Herein, we show that polydopamine (PDA), a well-known synthetic melanin, becomes an excellent trap for alkylperoxyl radicals (ROO^., typically formed during autoxidation of lipid substrates) in the presence of hydroperoxyl radicals (HOO^.). The key reaction explaining this peculiar antioxidant activity is the reduction of the ortho-quinone moieties present in PDA by the reaction with HOO^.. This reaction occurs via a H-atom transfer mechanism, as demonstrated by the large kinetic solvent effect of the reaction of a model quinone (3,5-di-tert-butyl-1,2-benzoquinone) with HOO^. (k=1.5×10⁷ and 1.1×10⁵ M⁻¹ s⁻¹ in PhCl and MeCN). The chemistry disclosed herein is an important step to rationalize the redox-mediated bioactivity of melanins and of quinones.

Ascertaining heat energy transfer is essential for the design of organic materials for energy conversion. For Y-series molecules, an extended backbone framework together with advantageous morphologies and suppressed structural disorder trigger more efficient heat diffusion properties. Higher thermal diffusivities enable better spread of phonons to relieve the thermal stress of organic semiconductor devices, leading to enhanced device thermal durability.

Abstract

Efficient heat transfer is beneficial to heat dissipation and the thermal durability of organic solar cell (OSCs). In this regard, heat transfer properties of organic semiconductors within OSCs should play important roles, but their thermal properties are rarely explored. Here, heat diffusion properties of Y-series non-fullerene acceptors processing different DA′D framework, named BZ4F-5, BZ4F-6, and BZ4F-7 are probed; it is found that backbone rings extension from five- to six- and seven-membered-fused rings trigger longer phonon mean free path and higher thermal diffusivities (D) in their pristine solid films and bulk heterojunction blends. Particularly, the correlation between the thermal transport properties in Y-series acceptors and their backbone geometry, molecule stacking, and thin-film crystallinity is demonstrated. More importantly, both organic thin-film transistors and OSCs confirm that thermal durability of organic semiconductor devices correlated with the thermal properties of their active layer. Although BZ5F-6 and BZ4F-7 based devices possess similar device performance at room temperature, superior heat dissipation in BZ4F-7 molecule endows it with enhanced device lifetime. These results contribute to critical design criteria for future molecular optimization in photovoltaic and optoelectronic devices.

A new urea-ammonium thiocyanate (UAT) molten salt was introduced as the additive in all-inorganic cesium lead triiodide solar cell, as a modification strategy to fully release and exploit coordination activities of SCN⁻ to deposit high-quality CsPbI₃ film. Thus, the UAT-based devices can provide an encouraging PCE up to 20.08 % with excellent operational stability of over 1000 h.

Abstract

Besides widely used surface passivation, engineering the film crystallization is an important and more fundamental route to improve the performance of all-inorganic perovskite solar cells. Herein, we have developed a urea-ammonium thiocyanate (UAT) molten salt modification strategy to fully release and exploit coordination activities of SCN⁻ to deposit high-quality CsPbI₃ film for efficient and stable all-inorganic solar cells. The UAT is derived by the hydrogen bond interactions between urea and NH₄ ⁺ from NH₄SCN. With the UAT, the crystal quality of the CsPbI₃ film has been significantly improved and a long single-exponential charge recombination lifetime of over 30 ns has been achieved. With these benefits, the cell efficiency has been promoted to over 20 % (steady-state efficiency of 19.2 %) with excellent operational stability over 1000 h. These results demonstrate a promising development route of the CsPbI₃ related photoelectric devices.

Herein, a semitransparent flexible MAPbBr₃ perovskite solar cell is demonstrated to be the roof of a greenhouse. It demonstrates a power conversion efficiency (PCE) of 7.67% with an average transmittance of ≈60% in the range of 540–760 nm.

Perovskite photovoltaics (PV) is an emerging thin-film solar energy technology that is advantageous over the currently dominant crystalline silicon PV in terms of its adjustable bandgap with sub-bandgap transparency, potential flexibility, and more rapid continuous roll-to-roll manufacturing, showing promise for unique niche applications. Herein, methylammioun lead tribromide (MAPbBr₃) is utilized in a semitransparent flexible solar cell with a transparent electrode using a sandwiched MoO₃/Au/MoO₃ (MAM) multilayer to harvest around 80% of the visible light region. Through design of the thickness of the MAM multilayer, the reflected light loss is significantly reduced, thereby improving the light transmittance in the visible light region to maximize the photosynthetic yield. The semitransparent flexible device exhibits a power conversion efficiency (PCE) of 7.67% (the highest efficiency of MAPbBr₃-based semitransparent flexible devices), and the opaque rigid MAPbBr₃ solar cell shows a PCE of 9.73% with a high open-circuit voltage of 1.629 V. Optical measurement demonstrates that the flexible cell without metal electrode shows over 77% transparency in the 540–1100 nm range, whereas the overall semitransparent cell shows an average transmittance of 60% in the 540–760 nm range, which is perfect for greenhouse vegetation to not only act as protective coverage but also provide practical output power.

Herein, drift-diffusion simulation parameters are established to describe efficient (20%) p–i–n-type perovskite solar cells. Using these parameters, effective strategies to further improve the performance are explored. It is found that the key to reaching the 30% efficiency milestone is maximizing the built-in voltage across the perovskite layer by implementing doped- or ultrathin transport layers such as self-assembled monolayers.

Perovskite semiconductors have demonstrated outstanding external luminescence quantum yields, enabling high power conversion efficiencies (PCEs). However, the precise conditions to advance to an efficiency regime above monocrystalline silicon cells are not well understood. Herein, a simulation model that describes efficient p–i–n-type perovskite solar cells well and a range of different experiments is established. Then, important device and material parameters are studied and it is found that an efficiency regime of 30% can be unlocked by optimizing the built-in voltage across the perovskite layer using either highly doped (10¹⁹ cm⁻³) transport layers (TLs), doped interlayers or ultrathin self-assembled monolayers. Importantly, only parameters that have been reported in recent literature are considered, that is, a bulk lifetime of 10 μs, interfacial recombination velocities of 10 cm s⁻¹, a perovskite bandgap ( E gap ) of 1.5 eV, and an external quantum efficiency (EQE) of 95%. A maximum efficiency of 31% is predicted for a bandgap of 1.4 eV. Finally, it is demonstrated that the relatively high mobile ion density does not represent a significant barrier to reach this efficiency regime. The results of this study suggest continuous PCE improvements until perovskites may become the most efficient single-junction solar cell technology in the near future.

Efficient ternary thick-film organic photovoltaics (OPVs) are fabricated using PM6 as the donor and BP4T-4F and BP3T-4F with symmetric and asymmetric structures as alloyed acceptors. The power conversion efficiency (PCE) of ternary OPVs is slightly decreased from 16.91% to 16.03% for active layer thickness 100–300 nm, exhibiting an excellent PCE tolerance on active layer thickness.

High-performance organic photovoltaics (OPVs) with relatively thick active layers are essential for large-scale production. Herein, series of OPVs with different active layer thicknesses are fabricated using PM6 as the donor and BP4T-4F and BP3T-4F with symmetric and asymmetric structures as acceptors. With the active layer thickness increasing from 100 to 300 nm, the power conversion efficiency (PCE) of BP3T-4F-based binary OPVs is slightly decreased from 15.37% to 14.40%, while the PCEs of BP4T-4F-based binary OPVs are markedly decreased from 16.89% to 14.99%. The two kinds of binary OPVs exhibit distinct PCEs and thickness tolerance features, which may be recombined into ternary OPVs using compatible BP3T-4F and BP4T-4F as alloyed acceptors. The ternary OPVs exhibit a slightly decreased PCE from 16.91% to 16.03% along with active layer thickness from 100 to 300 nm, benefiting from the well-optimized phase separation in ternary active layers. It is worth highlighting that the fill factor (FF) of 71.47% is achieved in ternary thick-film OPVs. The PCE of 16.03% and FF of 71.47% should be among the highest values among OPVs with 300 nm thick active layers.

Healable and recyclable elastomers with superhigh strength (tensile strength ≈ 75.6 MPa, true stress at break ≈ 1.21 GPa) and ultrahigh toughness (≈390.2 MJ m⁻³) are reported. The elastomer has unprecedented crack tolerance with fracture energy of 215.2 kJ m⁻² that even exceeds that of metals and alloys. The elastomer exhibits superhigh elastic restorability allowing dimensional recovery from elongation over 12 times.

Abstract

Spider silk is one of the most robust natural materials, which has extremely high strength in combination with great toughness and good elasticity. Inspired by spider silk but beyond it, a healable and recyclable supramolecular elastomer, possessing superhigh true stress at break (1.21 GPa) and ultrahigh toughness (390.2 MJ m⁻³), which are, respectively, comparable to and ≈2.4 times higher than those of typical spider silk, is developed. The elastomer has the highest tensile strength (ultimate engineering stress, 75.6 MPa) ever recorded for polymeric elastomers, rendering it the strongest and toughest healable elastomer thus far. The hyper-robust elastomer exhibits superb crack tolerance with unprecedentedly high fracture energy (215.2 kJ m⁻²) that even exceeds that of metals and alloys, and superhigh elastic restorability allowing dimensional recovery from elongation over 12 times. These extraordinary mechanical performances mainly originate from the meticulously engineered hydrogen-bonding segments, consisting of multiple acylsemicarbazide and urethane moieties linked with flexible alicyclic hexatomic spacers. Such hydrogen-bonding segments, incorporated between extensible polymer chains, aggregate to form geometrically confined hydrogen-bond arrays resembling those in spider silk. The hydrogen-bond arrays act as firm but reversible crosslinks and sacrificial bonds for enormous energy dissipation, conferring exceptional mechanical robustness, healability, and recyclability on the elastomer.