Yingzhi Jin

A cold-aging induced aggregation approach is demonstrated to enhance device efficiency of organic solar cells via tuning of the pre-aggregates of polymer donor PM6 in solution and therefore in its solid photovoltaic blend films with a range of fused-ring and non-fused-ring non-fullerene electron acceptors.

Abstract

The molecular ordering and pre-aggregation of photovoltaic materials in solution can significantly affect the nanoscale morphology in solid photoactive layers, and play a vital role in determining the power conversion efficiency (PCE) of organic solar cells (OSCs). Herein, a cold-aging strategy is reported to mediate the pre-aggregation of PM6 polymer in solution through a disorder-order transition, which leads to dense and fine PM6 aggregates with enhanced π−π stacking in its blend thin films with either fused-ring and non-fused-ring non-fullerene acceptors (NFAs) including Y6-BO, N3, IT-4F, and PTIC. The fine aggregates of PM6 and slightly enlarged NFA domains improve the continuous networks with enhanced and balanced charge mobility. The resulting OSCs all demonstrate enhanced PCEs compared to their counterparts without any cold-aging treatments, with PM6:Y6-BO OSC being most effective from 16.6% to 17.7%, demonstrating the universality of this approach. This can be further optimized upon casting of the cold-aging solution with the presence of solvent vapor, resulting in a champion PCE of 18.0% for PM6:Y6-BO OSC, which is the highest PCE of this OSC reported in the literature. This work provides a rational guide for optimizing non-fullerene OSCs via aggregation control before and during the solution casting process.

This work reports a novel n-type organic passivator for SnO₂, via regulation of the molecular structures toward efficient charge transport and suppressed recombination at the SnO₂/perovskite interfaces. An impressive power conversion efficiency over 23% is achieved by the resulting perovskite solar cells.

Abstract

SnO₂ has been universally applied as electron transporting layer (ETL) towards the fabrication of highly efficient perovskite solar cells (PSCs), owing to its unique advantages including low-temperature solution-processability, high optical, transmittance and good electrical conductivity. Uncoordinated Sn-dangling bonds on SnO₂ surface exist as deep traps to capture the photogenerated carriers, causing hysteresis and device instability. Fullerene derivatives, though being widely utilized as the passivator for SnO₂, are highly prone to self-aggregate due to their π-cage structures, which hampers passivation. Herein, π-conjugated n-type small molecules with better film formation ability are innovatively designed, to improve passivation effectiveness. By exploring the interplay between molecular stacking of small molecules and charge transporting/recombination dynamics at the SnO₂/perovskite interface, it is unveiled that a more compact molecular packing of the organic passivators yields superior interfacial characteristics, in terms of fewer trap states, lower charge recombination and higher electron transporting efficiency. An impressive PCE over 23% is achieved with the assistance of this new-type SnO₂-passivator, which is among the highest reported value for triple-cation perovskite systems to date. This work offers an original concept for the design and synthesis of ETL passivators towards the development of high performance and stable PSCs.

The multi-scale defect repair strategy is developed to fabricate scalable and flexible perovskite solar cells. By inhibiting the aggregation behavior of colloidal particles to avoid pinholes and intergranular cracking in the perovskite film, along with repairing the deep defects at the interface, the target flexible devices (1.01 cm²) deliver a superior efficiency of 18.12% with improved air atmosphere stability.

Abstract

Homogeneity and stability of flexible perovskite solar cells (PSCs) are significant for the commercial feasibility in upscaling fabrication. Concretely, the mismatching between bottom interface and perovskite precursor ink can cause uncontrollable crystallization and undesired dangling bonds during the printing process. Herein, methylammonium acetate, serving as ink assistant (IAS) can effectively avoid the micron-scale defects of perovskite film. The in situ optical microscope is applied to prove the IAS can inhibit the colloidal aggregation and induce more adequate crystallization growth, thus avoiding the micron-scale defects of pinholes and intergranular cracking. Concurrently, 4-chlorobenzenesulfonic acid is introduced into the electrode surface as a passivation layer to restore the deep traps at perovskite interface in nano-scale. Finally, the target flexible devices (1.01 cm²) deliver a superior efficiency of 18.12% with improved air atmosphere stability. This multi-scale defect repair strategy provides an integrated design concept of homogeneity and stability for scalable and flexible PSCs.

Mold-Assisted Decal-Coating

In article number 2103705, Thuc-Quyen Nguyen, Dong Hwan Wang, and co-workers present a photos ensitive layer based on non-fullerene-acceptors for efficient near-infrared photodetection and power conversion developed via novel decal-coating by introducing an adhesion-controlled polymer mold. The decal-coating induces selective charge transport and suppresses noise current owing to morphology inversion, compared to conventional spin-coating. Furthermore, the devices with decal-coating demonstrate exceptional operation stability.

A poly(3,4-ethylenedioxythiophene):poly-(styrenesulfonate) (PEDOT:PSS)-free organic solar cell (OSC) architecture is successfully constructed by employing a binary solvent-chlorinated indium tin oxide anode, which can simultaneously improve the device performance and operational stability of non-fullerene OSCs.

Abstract

Despite the tremendous development of different high-performing photovoltaic systems in non-fullerene polymer solar cells (PSCs), improving their performance is still highly demanding. Herein, an effective and compatible strategy, i.e., binary-solvent-chlorinated indium tin oxide (ITO) anode, is presented to improve the device performance of the state-of-the-art photoactive systems. Although both ODCB (1,2-dichlorobenzene) solvent- and ODCB:H₂O₂ (hydrogen peroxide) co-solvent-chlorinated ITO (ITO-Cl_-ODCB and ITO-Cl_-ODCB:H2O2) show similar optical transmittance, electrical conductivities, and work function values, ITO-Cl_-ODCB:H2O2 exhibits higher Cl surface coverage and more suitable surface free energy close to the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-buffered ITO anode (ITO/PEDOT:PSS). As a direct consequence, the performance of ITO-Cl_-ODCB-based PBDB-T-2F:BTP-eC9:PC₇₁BM PSCs is comparable as the bare ITO-based devices. In contrast, the performance of ITO-Cl_-ODCB:H2O2-based devices with both small and the scaled-up areas significantly surpass the ITO/PEDOT:PSS-based devices. Furthermore, detailed experimental studies are conducted linking optical property, blend morphology, and physical dynamics to find the reasons for the performance difference. By applying the ITO-Cl_-ODCB:H2O2 anode to six other photovoltaic systems, the device efficiencies are enhanced by 3.6–6.2% relative to those of the ITO/PEDOT:PSS-based control devices, which validates its great application potential of co-solvent-modified ITO anode employed into PEDOT:PSS-free PSCs.

An aggregation-induced emission-active multifunctional phototheranostic system is reported through intentional control of the side-chain structure. Bearing the longest alkyl chain, all of those three energy dissipation pathways are retained controllably. In vitro and in vivo evaluations verify that TBFT2 nanoparticles perform well in terms of fluorescence imaging-guided photodynamic and photothermal therapy synergistic cancer therapy.

Abstract

The ingenious construction of versatile cancer phototheranostics involving fluorescence imaging (FLI) and photodynamic and photothermal therapies (PDT, PTT) concurrently has attracted great interest. By virtue of their inherent twisted structures and plentiful motion moieties, aggregation-induced emission luminogens (AIEgens) have been proven to be perfect templates for the development of multimodal phototheranostic systems as their diverse energy consumption pathways can be flexibly regulated through tuning the intramolecular motions. Side-chain engineering is generally accepted as a useful regulation strategy for intramolecular motions through altering the side-chain structure of the molecule, but has rarely been reported for the construction of AIE-active multimodal phototheranostics. Herein, by taking full advantage of the side-chain engineering strategy, an AIE-active multifunctional phototheranostic system (TBFT2 nanoparticles) is successfully constructed by intentionally manipulating the length of side chains. Bearing the longest alkyl chain, all of those three energy dissipation pathways including radiative decay, nonradiative thermal deactivation, and intersystem crossing process of TBFT2 are retained simultaneously and controllably in the aggregate state. In vitro and in vivo evaluations verify that TBFT2 nanoparticles perform well in terms of FLI-guided PDT and PTT synergistic cancer therapy. This study thus provides new insight into the exploration of superior versatile phototheranostics through side-chain engineering.

The Förster resonance energy transfer between two molecules can facilitate the high-lying reverse intersystem crossing process in aggregation-induced emission and hybridized local and charge-transfer hosts, thereby reducing the loss from T _n to T _{n −1} state and improving exciton utilization, and finally realizing the efficiency breakthrough of blue fluorescence organic light-emitting diodes.

Abstract

Aggregation-induced emission (AIE) and hybridized local and charge-transfer (HLCT) materials are two kinds of promising electroluminescence systems for the fabrication of high-efficiency organic light-emitting diodes (OLEDs) by harnessing “hot excitons” at the high-lying triplet exciton states (T _n , n ≥ 2). Nonetheless, the efficiency of the resulting OLEDs did not meet expectations due to the possible loss of T _n →T _{n −1}. Herein, experimental results and theoretical calculations demonstrate the “hot exciton” process between the high-lying triplet state T₃ and the lowest excited singlet state S₁ in an AIE material 4⁗-(diphenylamino)-2″,5″-diphenyl-[1,1″:4′,1″:4″,1′″:4′″,1⁗-quinquephenyl]-4-carbonitrile (TPB-PAPC) and it is found that the Förster resonance energy transfer (FRET) between two molecules can facilitate the “hot exciton” process and inhibit the T₃→T₂ loss by doping a blue fluorescent emitter in TPB-PAPC. Finally, the doped TPB-PAPC blue OLEDs achieve a maximum external quantum efficiency (EQE_max) of 9.0% with a small efficiency roll-off. Furthermore, doping the blue fluorescent emitter in a HLCT material 2-(4-(10-(3-(9H-carbazol-9-yl)phenyl)anthracen-9-yl)phenyl)-1-phenyl-1H-phenanthro[9,10-d] imidazole (PAC) is used as the emission layer, and the resulting blue OLEDs exhibit an EQE_max of 17.4%, realizing the efficiency breakthrough of blue fluorescence OLEDs. This work establishes a physical insight in the design of high-performance “hot exciton” molecules and the fabrication of high-performance blue fluorescence OLEDs.

The complicated intermolecular interactions in bulk-heterojunction (BHJ) play a fundamental role in organic photovoltaics. This study implies that the interactions between acceptors (A/A) and donor/acceptor (D/A) interactions synergistically control the nanoscale networks of BHJ and exciton/charge behaviors. Therefore, balancing these two kinds of intermolecular interactions should be well considered for constructing high performance organic photovoltaics.

Abstract

Promoted by uninterrupted materials and device innovation, organic solar cells have achieved impressive development. However, the complicated intermolecular interactions inside active layers are less understood. Herein, the intermolecular interactions are studied from the dual perspectives of acceptor/acceptor (A/A) and donor/acceptor (D/A), and how these interactions synergistically control the final efficiencies. Three small molecular acceptors (SMAs) are designed with different end-caps, which manipulate the crystallinity and electrostatic potential (ESP) distributions of acceptors, and accordingly, the A/A and D/A intermolecular interactions. The results show that SMA LA17 with low A/A interactions exhibits inferior performance around 12%, owing to its strong D/A interaction with donor PM6, which shapes too miscible morphology and increases charge recombination. Instead, LA16 with strong A/A interactions and moderate D/A interactions delivers improved bulk-heterojunction (BHJ) networks, and therefore, enhances charge transport and diminishes geminate or trap-assisted charge recombination. Consequently, PM6:LA16 records the competitive efficiency of up to 13.74% among the three systems. Therefore, this study deepens the synergistic or balancing effect of the D/A and A/A interactions on BHJ blends for efficient organic solar cells.

The recent progress in lead-free double perovskite Cs₂AgBiBr₆ is comprehensively reviewed. The fundamental properties are systematically discussed and the achievements in Cs₂AgBiBr₆ related applications are highlighted. Moreover, the challenges in Cs₂AgBiBr₆ materials and applications are emphasized, and perspectives for future research in this field are provided.

Abstract

Cs₂AgBiBr₆, as a benchmark lead-free double perovskite, has emerged as a promising alternative to lead-based perovskites because of its high stability, non-toxicity, exceptional optoelectronic properties, and multifunctionality. To encourage further research on Cs₂AgBiBr₆ and its broad applications, in this review, its fundamental properties including the structure-property relation, synthesis, stability, origin of absorption and photoluminescence, electron-phonon coupling, role of defects, charge carrier dynamics, and bandgap modulation are comprehensively emphasized. The recent progress on the wide applications including solar cells, light/X-ray detectors, and ferroelectric/magnetic devices are highlighted. Moreover, the challenges of Cs₂AgBiBr₆ materials and related applications are discussed and perspectives are provided for guiding the future development of this research area.

An organic-small-molecule solar-energy-absorbing material with a strong intramolecular charge transfer character and a conjugate rigid plane skeleton is developed, which exhibits a wide absorption spectrum of 300–850 nm for efficient solar energy harvesting and highly efficient water evaporation and thermoelectricity power generation.

Abstract

Recently, owing to the great structural tunability, excellent photothermal property, and strong photobleaching resistance, organic-small-molecule photothermal materials are proposed as promising solar absorbent materials. Herein, through fusing two strong electron-withdrawing units dibenzo[f,h]quinoxaline and anthraquinone units, a rigid planar acceptor dibenzo[a,c]naphtho[2,3-h]phenazine-8,13-dione (PDN) with stronger electron-withdrawing ability is obtained and used to construct donor–acceptor-type organic-small-molecule solar-energy-absorbing material, 2,17-bis(diphenylamino)dibenzo[a,c]naphtho[2,3-h]phenazine-8,13-dione (DDPA-PDN). The new compound exhibits a strong intramolecular charge transfer character and conjugates rigid plane skeleton, endowing it with a broadband optical absorption from 300 to 850 nm in the solid state, favorable photothermal properties, high photothermal conversion ability, and good photobleaching resistance. Under laser irradiation at 655 nm, the solid photothermal conversion efficiency of the resulting DDPA-PDN molecule reaches 56.23%. Additionally, DDPA-PDN-loaded cellulose papers equipped with abundant microchannels for water flow are integrated with thermoelectric devices, thus achieving an evaporation rate and voltage as high as 1.07 kg m⁻² h⁻¹ and 83 mV under 1 kW m⁻² solar irradiation, respectively. This study demonstrates the application of photothermal organic-small-molecules in water evaporation and power generation, therefore offering a valuable prospect of their utilization in solar energy harvesting.

Research on the stability of organic solar cells based on fused-ring electron acceptors (FREAs) is now becoming more urgent. This perspective focuses on discussing the possible degradation mechanisms of FREAs and effective strategies of enhancing their stability reported recently. Also, a conclusion and outlook for the future design of highly efficient and stable FREAs are presented.

Abstract

The power conversion efficiency of organic solar cells (OSCs) has made exceptionally rapid progress in the past five years owing to the emergence of fused-ring electron acceptors (FREAs). To achieve the commercialization, it is urgent to resolve the stability issues of OCSs from materials to devices. In particular, the state-of-the-art FREAs, often synthesized by Knoevenagel condensation, generally contain two exocyclic vinyl groups (CC bond) as the conjugated bridges, which inevitably exhibit an obvious electron-deficient characteristic due to the strong push-pull electronic effect. As a result, these vinyl bridges are vulnerable to nucleophile attacking and/or photooxidation, leading to poor chemical and photochemical stabilities of FREAs that easily cause the degradation of device performance. In this perspective, an in-depth understanding of the degradation mechanism of FREAs is provided, and then effective strategies reported recently are reviewed for improving the chemical and photochemical stabilities of FREAs from interfacial engineering to molecular engineering to additive engineering. Finally, a conclusion and outlook for the future design of highly efficient and stable FREAs are also presented.

Chlorination is an important strategy to explore the structure–property relationship of nonfullerene acceptors. BTIC-4Cl-TCl-γ with chlorine at the γ-position of the conjugated thiophene shows a 3D network structure while BTIC-4Cl-TCl-β is found to be reformed to a quasi-3D network, which promotes a champion open-circuit voltage of 0.86 V and has the highest efficiency (15.65%).

Abstract

Systematic investigation of three nonfullerene acceptors, BTIC-4Cl-T, BTIC-4Cl-TCl-γ, and BTIC-4Cl-TCl-b, with or without a chlorine substituent at the γ/b-position of the side chain thiophene ring, reveals that molecular planarity, stacking structure, and photovoltaic performance of the compounds are dependent on the position of the chlorine substituent. Of the materials using thiophenes in conjugated side chains, BTIC-4Cl-T shows a relatively lower open-circuit voltage of 0.81 V, decreased current density, leading to an efficiency of only 10.86%. BTIC-4Cl-TCl-γ with chlorine at the γ-position of the conjugated thiophene shows a 3D network structure, a greatly increased current density, and an efficiency of 14.35%. BTIC-4Cl-TCl-b, with a chlorine atom in b-position, is found to have been reformed to a quasi-3D network, in which electron hopping can be efficiently realized in adjacently positioned, linearly arranged molecules due to S···S interactions. With this quasi-3D network, BTIC-4Cl-TCl-b promotes the open-circuit voltage up to 0.86 V and has the highest efficiency (15.65%) among the three acceptors. These results prove that chlorination is an effective strategy to improve photovoltaic performance and highlights the decisive relationship between structural regulation and molecular arrangement. It also provides a good starting point for the exploration and design of next generation high-performance materials.

A hybrid planar/bulk heterojunction is constructed by introducing a p-type polymer (PTO3) and an n-type naphthalene imide (NDI-i8) on both sides of a mixed donor:acceptor active layer. The tailored hybrid heterojunction presents a decreased energy loss and improved efficiency. As a result, an outstanding PCE of 18.5% is achieved, which is among the top values in the field of organic solar cells.

Abstract

The donor:acceptor heterojunction has proved as the most successful approach to split strongly bound excitons in organic solar cells (OSCs). Establishing an ideal architecture with selective carrier transport and suppressed recombination is of great importance to improve the photovoltaic efficiency while remains a challenge. Herein, via tailoring a hybrid planar/bulk structure, highly efficient OSCs with reduced energy losses (E _losss) are fabricated. A p-type benzodithiophene-thiophene alternating polymer and an n-type naphthalene imide are inserted on both sides of a mixed donor:acceptor active layer to construct the hybrid heterojunction, respectively. The tailored structure with the donor near the anode and the acceptor near the cathode is beneficial for obtaining enhanced charge transport, extraction, and suppressed charge recombination. As a result, the photovoltaic characterizations suggest a reduced nonradiative E _loss by 25 meV, and the best OSC records a high efficiency of 18.5% (certified as 18.2%). This study highlights that precisely regulating the structure of donor:acceptor heterojunction has the potential to further improve the efficiencies of OSCs.

A new concept of innovative transmission cavities combined with organic photodetectors (OPDs) is proposed to achieve narrowband photodetection from the VIS to the NIR region. With this approach, an ultrahigh specific detectivity above 10¹⁴ Jones is achieved and is integrated into a miniaturized spectrometer, representing a significant step toward applying OPDs as an attractive alternative for mobile spectrometric sensing.

Abstract

Spectroscopic photodetection plays a key role in many emerging applications such as context-aware optical sensing, wearable biometric monitoring, and biomedical imaging. Photodetectors based on organic semiconductors open many new possibilities in this field. However, ease of processing, tailorable optoelectronic properties, and sensitivity for faint light are still significant challenges. Here, the authors report a novel concept for a tunable spectral detector by combining an innovative transmission cavity structure with organic absorbers to yield narrowband organic photodetection in the wavelength range of 400–1100 nm, fabricated in a full-vacuum process. Benefiting from this strategy, one of the best performed narrowband organic photodetectors is achieved with a finely wavelength-selective photoresponse (full-width-at-half-maximum of ≈40 nm), ultrahigh specific detectivity above 10¹⁴ Jones, the maximum response speed of 555 kHz, and a large dynamic range up to 168 dB. Particularly, an array of transmission cavity organic photodetectors is monolithically integrated on a small substrate to showcase a miniaturized spectrometer application, and a true proof-of-concept transmission spectrum measurement is successfully demonstrated. The excellent performance, the simple device fabrication as well as the possibility of high integration of this new concept challenge state-of-the-art low-noise silicon photodetectors and will mature the spectroscopic photodetection into technological realities.

Defect-triggered phase degradation has become the main issue in the field of inorganic CsPbI₃ perovskite. A crystal secondary growth of inorganic perovskites induced by a solid-state reaction to achieve defect compensation in CsPbI₃ perovskite is demonstrated. Finally, the defect-compensated CsPbI₃-based solar cell delivers 20.04% efficiency with excellent operational stability.

Abstract

Defect-triggered phase degradation is generally considered as the main issue that causes phase instability and limited device performance for CsPbI₃ inorganic perovskites. Here, a defect compensation in CsPbI₃ perovskite through crystal secondary growth of inorganic perovskites is demonstrated, and highly efficient inorganic photovoltaics are realized. This secondary growth is achieved by a solid-state reaction between a bromine salt and defective CsPbI₃ perovskite. Upon solid-state reaction, the Br⁻ ions can diffuse over the entire CsPbI₃ perovskite layer to heal the undercoordinated Pb²⁺ and conduct certain solid-state I/Br ion exchange reaction, while the organic cations can potentially heal the Cs⁺ cation vacancies through coupling with [PbI₆]⁴⁻ octahedra. The carrier dynamics confirm that this crystal secondary growth can realize defect compensation in CsPbI₃. The as-achieved defect-compensated CsPbI₃ not only improves the charge dynamics but also enhances the photoactive phase stability. Finally, the CsPbI₃-based solar cell delivers 20.04% efficiency with excellent operational stability. Overall, this work proposes a novel concept of defect compensation in inorganic perovskites through crystal secondary growth induced by solid-state reaction that is promising for various optoelectronic applications.

A green thermally activated delayed fluorescence (TADF) emitter with an extended π-system of linear donor (D)–acceptor (A)–donor (D) structure is established to simultaneously obtain a horizontal emitting dipole orientation ratio of 92%, a reverse intersystem crossing rate of 1.16 × 10⁶ s^–1 and a photoluminescence quantum yield of 95%, together affording a champion maximum external quantum efficiency of 39.1%.

Abstract

Thermally activated delayed fluorescence (TADF) emitters featuring preferential horizontal emitting dipole orientation (EDO) are in urgent demand for enhanced optical outcoupling efficiency in organic light-emitting diodes (OLEDs). However, simultaneously manipulating EDO and optoelectronic properties remains a formidable challenge. Here, an extended linear D–A–D structure with both enlarged donor (D) and acceptor (A) π-systems is established, not only elaborately manipulating parallel horizontal molecular orientation and EDO along its long axis by multi-driving-forces for a high horizontal dipole ratio (Θ _//), but also delocalizing distribution of frontier energy levels for optimized electronic properties. The proof-of-the-concept emitter simultaneously affords a high Θ _// of 92%, a high photoluminescence quantum yield of 95%, and a fast reverse intersystem crossing rate of 1.16 × 10⁶ s^-1. The corresponding OLED achieves a champion maximum external quantum efficiency of 39.1% among all green TADF devices without any external light-extraction techniques, together with a maximum power efficiency of 112.0 lm W^-1 and alleviated efficiency roll-off. These findings may inspire even better full-color TADF emitters that push the device efficiency toward the theoretical limits.

Nickel oxide (NiO _x ) nanoparticles with high crystallinity and good dispersibility by the polymer network micro-precipitation method is synthesized, and the colloidal solution of ionic liquid-assisted NiO _x NPs dispersion is used to fabricate high-quality NiO _x films. Ultimately, the 1.01 cm² perovskite devices with the optimized NiO _x layers achieve the champion power conversion efficiency of 20.91% and 19.17% on rigid and flexible substrates, respectively.

Abstract

As one of the most promising hole transport layers (HTLs), nickel oxide (NiO _x ) has received extensive attention due to its application in flexible large-area perovskite solar cells (PSCs). However, the poor interface contact caused by inherent easy-agglomeration phenomenon of NiO _x nanoparticles (NPs) is still the bottleneck for achieving high-performance devices. Herein, a general strategy to synthesize NiO _x NPs with high crystallinity and good dispersibility via the polymer network micro-precipitation method is reported. Promisingly, this approach realizes the flow-division of precipitant and the restraint of the NPs motion, thereby effectively alleviating the coagulation phenomenon caused by excessive local concentration and secondary movement adsorption. Furthermore, the addition of ionic liquid not only inhibits the secondary aggregation of NiO _x NPs during the dispersion process, but also significantly enhances the properties of the colloidal solution. Ultimately, the 1.01 cm² PSCs based on the optimized NiO _x HTLs achieve the champion power conversion efficiency of 20.91% and 19.17% on rigid and flexible substrates, respectively. Moreover, the reproducibility and stability of PSCs are also significantly improved, especially for flexible devices. Overall, this strategy provides the possibility for flexible, large-area fabrication of high-quality NiO _x HTLs to promote the development of stable and efficient perovskite devices.

The novel structurally defined and covalently linked donor–acceptor dyad 4 is implemented into single-material organic solar cells as the essential ambipolar and photoactive layer. The combination of an oligothiophene donor and PC₇₁BM fullerene as acceptor not only leads to enhanced 5.34% power conversion efficiency, but also to impressive long-term stability after 750 hours (one month) of continuous illumination.

Abstract

A novel donor–acceptor dyad, 4, in which the conjugated oligothiophene donor is covalently connected to fullerene PC₇₁BM by a flexible alkyl ester linker, is synthesized and applied as photoactive layer in solution-processed single-material organic solar cells (SMOSCs). Excellent photovoltaic performance, including a high short-circuit current density (J _SC) of 13.56 mA cm⁻², is achieved, leading to a power conversion efficiency of 5.34% in an inverted cell architecture, which is substantially increased compared to other molecular single materials. Furthermore, dyad 4-based SMOSCs display excellent stability maintaining 96% of the initial performance after 750 h (one month) of continuous illumination and operation under simulated AM 1.5G irradiation. These results will strengthen the rational molecular design to further develop SMOSCs for potential industrial application.

By designing new donor/acceptor materials and combining a ternary blending strategy, a maximum power conversion efficiency (PCE) of 19.0% (certified value of 18.7%) in single-junction organic photovoltaic (OPV) cells is achieved. It is demonstrated that finely tuning the light utilization and photophysical processes of the active layer has great potential for further improving the PCEs of OPV cells.

Abstract

Improving power conversion efficiency (PCE) is important for broadening the applications of organic photovoltaic (OPV) cells. Here, a maximum PCE of 19.0% (certified value of 18.7%) is achieved in single-junction OPV cells by combining material design with a ternary blending strategy. An active layer comprising a new wide-bandgap polymer donor named PBQx-TF and a new low-bandgap non-fullerene acceptor (NFA) named eC9-2Cl is rationally designed. With optimized light utilization, the resulting binary cell exhibits a good PCE of 17.7%. An NFA F-BTA3 is then added to the active layer as a third component to simultaneously improve the photovoltaic parameters. The improved light unitization, cascaded energy level alignment, and enhanced intermolecular packing result in open-circuit voltage of 0.879 V, short-circuit current density of 26.7 mA cm⁻², and fill factor of 0.809. This study demonstrates that further improvement of PCEs of high-performance OPV cells requires fine tuning of the electronic structures and morphologies of the active layers.

Inspired by the ordered structure of muscles, MXene conductive hydrogels are anisotropic and can be used as wearable flexible sensors. The conductive hydrogels have the advantages of wide temperature tolerance range, high sensitivity and good stability. The flexible sensors can achieve motion detection through wireless technology and can be assembled into 3D arrays.

Abstract

Conductive hydrogels as flexible electronic devices, not only have unique attractions but also meet the basic need of mechanical flexibility and intelligent sensing. How to endow anisotropy and a wide application temperature range for traditional homogeneous conductive hydrogels and flexible sensors is still a challenge. Herein, a directional freezing method is used to prepare anisotropic MXene conductive hydrogels that are inspired by ordered structures of muscles. Due to the anisotropy of MXene conductive hydrogels, the mechanical properties and electrical conductivity are enhanced in specific directions. The hydrogels have a wide temperature resistance range of −36 to 25 °C through solvent substitution. Thus, the muscle-inspired MXene conductive hydrogels with anisotropy and low-temperature resistance can be used as wearable flexible sensors. The sensing signals are further displayed on the mobile phone as images through wireless technology, and images will change with the collected signals to achieve motion detection. Multiple flexible sensors are also assembled into a 3D sensor array for detecting the magnitude and spatial distribution of forces or strains. The MXene conductive hydrogels with ordered orientation and anisotropy are promising for flexible sensors, which have broad application prospects in human–machine interface compatibility and medical monitoring.

Flexible and air-stable near-infrared (NIR) sensors are achieved based on solution-processed n-type In₂O₃/PTPBT-ET hybrid phototransistors, combining the advantages of both fast charge transport in metal oxide semiconductors and high NIR photoresponse of polymer semiconductors. The In₂O₃/PTPBT-ET phototransistor exhibits high electrical properties, robust mechanical flexibility, and outstanding NIR sensing performance, promising for large-area wearable NIR image sensor applications.

Abstract

Flexible and air-stable phototransistors are highly demanded for wearable near-infrared (NIR) image sensors. However, advanced NIR sensors via low-cost, solution-based processes remained a challenge. Herein, high-performance inorganic–organic hybrid phototransistors are achieved based on solution processed n-type metal oxide/polymer semiconductor heterostructures of In₂O₃/poly{5,5′-bis[3,5-bis(thienyl)phenyl]-2,2′-bithiophene-3-ethylesterthiophene]} (PTPBT-ET). The In₂O₃/PTPBT-ET hybrid phototransistor combines the advantages of both fast electron transport in In₂O₃ and high photoresponse in PTPBT-ET, showing high saturation mobility of 7.1 cm² V⁻¹ s⁻¹ and large current on/off ratio of >10⁷. As a result, the phototransistor exhibits high performance towards NIR light sensing with a responsivity of 200 A W⁻¹, a specific detectivity of 1.2 × 10¹³ Jones, and fast photoresponse with rise/fall time of 5/120 ms. Remarkably, the hybrid phototransistor, without any passivation, demonstrates excellent electrical stability without performance degradation even after 160 days in air. A 10 × 10 phototransistor array is also enabled by virtue of the high device uniformity. Lastly, flexible In₂O₃/PTPBT-ET phototransistor on polyimide substrate is attained, exhibiting outstanding mechanical flexibility up to 1000 bending/releasing cycles at a bending radius of 5 mm. These achievements pave the way for constructing air-stable hybrid phototransistors for flexible NIR image sensor applications.

Interlayer Spacing

In article number 2104007, Michael Naguib and co-workers report the engineering of interlayer spacing of multilayer MXene—by pre-intercalation of pillars—to host large-size cations of room temperature ionic liquids in between the layers, achieving high energy density supercapacitors. An optimum interlayer spacing of 2.2 nm (for pre-intercalated Ti₃C₂) allows for a capacitance of 257 F g⁻¹ (1428 mF cm⁻² and 492 F cm⁻³) over a 3.2 V potential window in 1-ethly-3-methylimidazolium bis-(trifluoromethylsulfonyl)-imide electrolyte.

Nature Energy, Published online: 29 July 2021; doi:10.1038/s41560-021-00880-z

Structural Color Images

In article number 2102451, Magnus P. Jonsson and co-workers demonstrate a new approach to produce dynamic structural colors with UV-patterned conducting polymers. The UV patterning controls the film thickness and polymer permittivity, and enables production of multicolor images with a single exposure step. Combined with the electrochemical tunability of the conducting polymer, these devices hold promise for next-generation multifunctional displays.

Narrowband photomultiplication-type organic photodetectors (PMOPDs) are prepared by employing one optical field adjusting (OFA) layer to adjust the optical filed distribution of the device and one photomultiplication layer for achieving photocurrent multiplication. The spectral response of narrowband PMOPDs can be tuned by different OFA layers, which is promising in achieving narrowband PMOPDs with a tunable spectral response.

Abstract

Narrowband photomultiplication-type organic photodetectors (PMOPDs) are realized with poly(3-hexylthiophene-2,5-diyl) (P3HT) as the optical field adjusting (OFA) layer and transfer-printed P3HT: [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) (50:1, w/w) as the photomultiplication (PM) layer. The thickness of the OFA layers is adjusted to optimize interfacial trapped electron distribution and density, which determines the external quantum efficiency (EQE) and spectral response range of PMOPDs. Narrowband PMOPDs with 2.5 µm thick P3HT as the OFA layer exhibit two narrow response peaks at 350 and 660 nm, and the corresponding EQE values at 350 and 660 nm are 180% and 760% under an applied bias of −20 V. A wide bandgap polymer poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (P-TPD) is deliberately incorporated into OFA layer for adjusting interfacial trapped electron distribution near Al electrode. Narrowband PMOPDs exhibit only one response peak at 660 nm with the enhanced EQE value of 1120% under the same bias. The enhanced EQE of PMOPDs with P-TPD is primarily attributed to the increased hole tunneling injection and transport, which can be ascribed to the enhanced trapped electron density near the Al electrode and the improved hole mobility, respectively. Clearly resolved images can be obtained from the imaging system with the narrowband PMOPDs as sensing pixel without any current preamplifier, indicating the promising potential of PMOPDs in imaging sense.

Efficient large-area flexible solar cells and modules are demonstrated based on a printable, transparent, low-surface-roughness, flexible electrode (silver nanowires:zinc-chelated polyethylenimine). A power conversion efficiency of 13.2% is obtained for a 54 cm² solar module. The flexible electrode is also demonstrated in high-performance flexible quantum-dot light-emitting diodes.

Abstract

Development of large-area flexible organic solar cells (OSCs) is highly desirable for their practical applications. However, the efficiency of the large-area flexible OSCs severely lags behind small-area devices. Here, efficient large-area flexible single cells with power conversion efficiency (PCE) of 13.1% and 12.6% for areas of 6 and 10 cm², and flexible modules with a PCE of 13.2% (54 cm²) based on poly(ethylene terephthalate)/Ag grid/silver nanowires (AgNWs):zinc-chelated polyethylenimine (PEI-Zn) composite electrodes are reported. The solution-processed flexible transparent electrode of AgNWs:PEI-Zn shows low surface roughness and good optoelectronic and mechanical properties. PEI-Zn is conductive and optically transparent. It can adhere to and wrap the AgNWs under electrostatic interaction between the negatively charged surface (AgNWs) and positively charged protonated amine groups (in PEI-Zn). It wraps the AgNWs networks and fills the void space to achieve a smooth surface. The flexible electrode is validated in both flexible OSCs and flexible quantum-dots light-emitting diodes (QLEDs). Small-area flexible OSCs show a PCE of 16.1%, and flexible QLEDs show an external quantum efficiency of 13.3%. In the end, a flexible module is demonstrated to charge a mobile phone as a flexible power source (shown in Video S1, Supporting Information).

Quasiplanar heterojunction (Q-PHJ) organic solar cells (OSCs) based on D18 and BTIC-BO-4Cl with a 3D network are reported, yielding a high power conversion efficiency (PCE) of 17.60%. The results show that the Q-PHJ architecture can replace the bulk heterojunction (BHJ) architecture to realize excellent OSCs for certain unique donors and acceptors, giving an alternative approach for photovoltaic material design and device fabrication.

Abstract

Bulk heterojunction (BHJ) organic solar cells (OSCs) have achieved great success because they overcome the shortcomings of short exciton diffusion distances. With the progress in material innovation and device technology, the efficiency of BHJ devices is continually being improved. For some special photovoltaic material systems, it is difficult to manipulate the miscibility and morphology of blend films, and this results in moderate, even poor device performance. Quasiplanar heterojunction (Q-PHJ) OSCs have been proposed to exploit the excellent photovoltaic properties of these materials. An OSC with BTIC-BO-4Cl has a 3D interpenetrating network structure with multiple channels that can facilitate the exciton diffusion and charge transport, and BTIC-BO-4Cl is therefore a good candidate for Q-PHJ OSCs. In this work, a D18:BTIC-BO-4Cl-based Q-PHJ device is fabricated. The exciton diffusion lengths of D18 and BTIC-BO-4Cl are in accord with the requirements of the Q-PHJ device and the efficiency of Q-PHJ device is as high as 17.60%. This study indicates that the Q-PHJ architecture can replace the BHJ architecture to produce excellent OSCs for certain unique donors and acceptors, providing an alternative approach to photovoltaic material design and device fabrication.

A regioregular narrow-bandgap n-type polymer, L15, is synthesized, showing higher electron mobility and larger absorption coefficient compared to its random analog. When applied as an electron acceptor in all-polymer solar cells (all-PSCs), L15 yields outstanding efficiencies of 15.2% and 16.2% in binary and ternary all-PSCs, respectively.

Abstract

Narrow-bandgap n-type polymers with high electron mobility are urgently demanded for the development of all-polymer solar cells (all-PSCs). Here, two regioregular narrow-bandgap polymer acceptors, L15 and MBTI, with two electron-deficient segments are synthesized by copolymerizing two dibrominated fused-ring electron acceptors (FREA) with distannylated aromatic imide, respectively. Taking full advantage of the FREA and the imide, both polymer acceptors show narrow bandgap and high electron mobility. Benefiting from the more extended absorption, better backbone ordering, and higher electron mobility than those of its regiorandom analog, the L15-based all-PSC yields a high power conversion efficiency (PCE) of 15.2% when blended with the polymer donor PM6. More importantly, MBTI incorporating a benzothiophene-core FREA segment shows relatively higher frontier molecular orbital levels than L15, forming a cascade-like energy level alignment with L15 and PM6. Based on this, ternary all-PSCs are designed where MBTI is introduced as a guest into the PM6:L15 host system. Thanks to further optimal blend morphology and more balanced charge transport, the PCE is improved up to 16.2%, which is among the highest values for all-PSCs. The results demonstrate that combining an FREA and an aromatic imide to construct regioregular narrow-bandgap polymer acceptors provides an effective approach to fabricate highly efficient all-PSCs.