以昇陳

The white organic light‐emitting diode (WOLED) harnessing fluorescence emitters can date back to 1995. However, the device efficiency is strictly limited due to the lack of triplets' utilization. By rationally allocating singlets and triplets to the corresponding channels with new host and new device architecture, a high‐efficiency all‐fluorescence WOLED is successfully achieved with analysis of the exciton diffusing.

Abstract

White organic light‐emitting diodes (WOLEDs) composed of conventional fluorophores possess color purity, low efficiency roll‐off, and rare metal absence, but suffer from theoretical limits due to the lack of triplet utilization. Due to the different diffusion distance for singlets and triplets, multiple Förster resonance energy transfer (FRET) channels can be adequately built up. Herein, besides the complementary component, a blue fluorescence layer, hosted by pure hydrocarbon material SF4‐TPE, is put forward as the spatial exciton manipulating layer to rationally allocate singlets and triplets to the corresponding channels. Hence, singlets are captured by the blue fluorophore, diffused triplets subsequently undergo energy resonance between the blue fluorophore and green assistant, and up‐conversion effect for eventual emission from the yellow fluorophore. Owing to the utilization of singlets and triplets, all‐fluorescence WOLEDs exhibit high efficiency exceeding 20%, with slight efficiency roll‐off even under high luminance of 5000 cd cm⁻². Moreover, CIE coordinates can be surrounding and precisely inside the American National Standard Institute (ANSI) quadrangles, as well as outstanding color stability (ΔCIE‐(x, y) within (0.001, 0.012)) from 300 to 13000 cd cm⁻².

A simple yet general strategy is proposed to develop sensitizing agents for effective near‐infrared‐triggered dual phototherapy of cancer based on an acceptor–donor–acceptor structured small molecule. The biocompatible nanoparticles, FA‐CNPs, present high photothermal conversion efficiency (PCE = 36.5%) and efficient ¹O₂ generation capacity (Φ = 18.6%) under single 808 nm laser irradiation.

Abstract

Dual phototherapy, including photodynamic therapy (PDT) and photothermal therapy (PTT), is regarded as a more effective method for cancer treatment than single PDT or PTT. However, development of single component and near‐infrared (NIR) triggered agents for efficient dual phototherapy remains a challenge. Herein, a simple strategy to develop dual‐functional small‐molecules‐based photosensitizers for combined PDT and PTT treatment is proposed through: 1) finely modulating HOMO–LUMO energy levels to regulate the intersystem crossing (ISC) process for effective singlet oxygen (¹O₂) generation for PDT; 2) effectively inhibiting fluorescence via strong intramolecular charge transfer (ICT) to maximize the conversion of photo energy to heat for PTT or ISC process for PDT. An acceptor–donor–acceptor (A‐D‐A) structured small molecule (CPDT) is designed and synthesized. The biocompatible nanoparticles, FA‐CNPs, prepared by encapsulating CPDT directly with a folate functionalized amphipathic copolymer, present strong NIR absorption, robust photostability, cancer cell targeting, high photothermal conversion efficiency as well as efficient ¹O₂ generation under single 808 nm laser irradiation. Furthermore, synergistic PDT and PTT effects of FA‐CNPs in vivo are demonstrated by significant inhibition of tumor growth. The proposed strategy may provide a new approach to reasonably design and develop safe and efficient photosensitizers for dual phototherapy against cancer.

An ultrahigh‐efficiency red thermally activated delayed fluorescence (TADF) OLED with an external quantum efficiency of nearly 28% and a power efficiency of exceeding 50 lm W⁻¹ is realized. The OLEDs incorporate excellent red TADF emitters simultaneously exhibiting 95% photoluminescence quantum efficiency and preferentially horizontal emitting dipole orientation.

Abstract

The development of red thermally activated delayed fluorescence (TADF) emitters having excellent optoelectronic properties and satisfactory electroluminescence efficiency is full of challenges due to strict molecular design principles. Two red TADF molecules, 3‐(9,9‐dimethylacridin‐10(9H)‐yl)acenaphtho[1,2‐b]quinoxaline‐9,10‐dicarbonitrile and 3‐(2,7‐dimethyl‐10H‐spiro[acridine‐9,9′‐fluoren]‐10‐yl)acenaphtho[1,2‐b]quinoxaline‐9,10‐dicarbonitrile, are developed by adopting a donor–acceptor molecular architecture bearing an electron‐accepting acenaphtho[1,2‐b]quinoxaline‐9,10‐dicarbonitrile (ANQDC) moiety and a 9,9‐dimethyl‐9,10‐dihydroacridine or 2,7‐dimethyl‐10H‐spiro[acridine‐9,9′‐fluorene] electron donor. The combined effects of rigid and planar D/A moieties and highly steric hindrance between D and A groups endow both molecules with high rigidity to suppress nonradiative decay processes, resulting in high photoluminescence quantum efficiencies (Φ_PLs) of up to 95%. Attributed to the linear and planar acceptor motif and rod‐like molecular configuration, both emitters achieve high horizontal ratios of emitting dipole orientation of ≈80%. The organic light‐emitting diodes (OLEDs) based on both emitters exhibit red emissions peaking at ≈615 nm and successfully afford ultrahigh electroluminescence performance with an external quantum efficiency of nearly 28% and a power efficiency of above 50 lm W⁻¹, on par with the state‐of‐the‐art device efficiency for red TADF OLEDs. This presents a feasible design strategy for excellent TADF emitters simultaneously possessing high Φ_PLs and horizontally aligned emitting dipoles.

A novel fluorinated n‐type small molecule diFIDT‐di(C(CN)₂) that displays unipolar electron mobility up to 0.49 cm² V⁻¹ s⁻¹ along with good retention of performance in ambient conditions in solution‐processed organic field‐effect transistors is reported. Fluorination is found to cause a surprisingly dramatic improvement in solubility, which is attributed to the increased van der Waals radius of fluorine inducing distortion of the π‐conjugated system.

Abstract

The synthesis of a novel fluorinated n‐type small molecule based on an indacenodithiophene core is reported. Fluorination is found to have a significant impact on the physical properties, including a surprisingly dramatic improvement in solubility, in addition to effectively stabilizing the lowest‐unoccupied molecular orbital energy (−4.24 eV). Single‐crystal analysis and density functional theory calculations indicate the improved solubility can be attributed to backbone torsion resulting from the positioning of the fluorine group in close proximity to the strongly electron‐withdrawing dicyanomethylene group. Organic thin‐film transistors made via blade coating display high electron mobility (up to 0.49 cm² V⁻¹ s⁻¹) along with good retention of performance in ambient conditions.

A multifunctional luminogen with delayed fluorescence can serve as emitter and host in organic light‐emitting diodes (OLEDs). As an emitter, it affords external quantum efficiencies (η_exts) of up to 20.1/24.5% for nondoped/doped OLEDs. As a host it provides excellent η_exts of up to 26.8%/21.0% for orange phosphorescent OLEDs/hybrid warm‐white OLEDs.

Abstract

Increasing exciton utilization and reducing exciton annihilation are crucial to achieve high performance of organic light‐emitting diodes (OLEDs), which greatly depend on molecular engineering of emitters and hosts. A novel luminogen (SBF‐BP‐DMAC) is synthesized and characterized. Its crystal and electronic structures, thermal stability, electrochemical behavior, carrier transport, photoluminescence, and electroluminescence are investigated. SBF‐BP‐DMAC exhibits enhanced photoluminescence and promotes delayed fluorescence in solid state and bipolar carrier transport ability, and thus holds multifunctionality of emitter and host for OLEDs. Using SBF‐BP‐DMAC as an emitter, the nondoped OLEDs exhibit maximum electroluminescence (EL) efficiencies of 67.2 cd A⁻¹, 65.9 lm W⁻¹, and 20.1%, and the doped OLEDs provide maximum EL efficiencies of 79.1 cd A⁻¹, 70.7 lm W⁻¹, and 24.5%. A representative orange phosphor, Ir(tptpy)₂acac, is doped into SBF‐BP‐DMAC for OLED fabrication, giving rise to superior EL efficiencies of 88.0 cd A⁻¹, 108.0 lm W⁻¹, and 26.8% for orange phosphorescent OLEDs, and forward‐viewing EL efficiencies of 69.3 cd A⁻¹, 45.8 lm W⁻¹, and 21.0% for two‐color hybrid warm‐white OLEDs. All of these OLEDs can retain high EL efficiencies at high luminance, with very small efficiency roll‐offs. The outstanding EL performance demonstrates the great potentials of SBF‐BP‐DMAC in practical display and lighting devices.

A new nonfullerene acceptor (NFA) with acceptor–donor–acceptor (A–D–A) architecture, i‐IEICO‐2F, is designed and synthesized. Devices based on i‐IEICO‐2F exhibit optimized photovoltaic performance with a power conversion efficiency (PCE) of 11.28%. Devices are found to be thermally stable and maintain 44% of their initial PCE after 184.5 h of continuous thermal annealing treatment at 150 °C.

Abstract

A nonfullerene acceptor (NFA) with acceptor–donor–acceptor (A–D–A) architecture, i‐IEICO‐2F, based on 4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene as an electron‐donating core and 2‐(6‐fluoro‐2,3‐dihydro‐3‐oxo‐1H‐inden‐1‐ylidene)‐propanedinitrile as electron‐withdrawing end groups, is designed and synthesized. i‐IEICO‐2F has a twist structure in the main conjugated chain, which causes blueshifted absorption and leads to harmonious absorption with a high bandgap donor. The bandgap of i‐IEICO‐2F compliments the bandgap of suitable wide bandgap donor polymers such as J52, leading to complete light absorption throughout the visible spectrum. Devices based on i‐IEICO‐2F exhibit optimized photovoltaic performance including an open‐circuit voltage of 0.93 V, a short‐circuit current density of 16.61 mA cm⁻², and a fill factor of 73%, and result in a power conversion efficiency (PCE) of 11.28%. The i‐IEICO‐2F‐based devices reach PCEs of >11% without using any additives or post‐treatments. Devices are found to be thermally stable and maintain 44% of their initial PCE after 184.5 h of continuous thermal annealing (TA) treatment at 150 °C. Based on UV, atomic force microscopy (AFM), and grazing incidence wide angle X‐ray scattering (GIWAXS) results, i‐IEICO‐2F devices show almost identical morphology and molecular orientation throughout the TA treatment and excellent stability compared to other IEICO derivatives.

The effects of the donating ability and bulkiness of the fluorenyl‐based donor in donor–π–acceptor structured organic dyes are investigated to establish the structure–property relationship in terms of molecular properties and photovoltaic performance. Through a simple cock‐tailed co‐sensitization strategy with porphyrin dye, the state‐of‐the‐art efficiencies of 14.2% and 11.6% with cobalt and iodine electrolytes, respectively, are achieved.

Abstract

A new series of 4‐hexyl‐4H‐thieno[3,2‐b]indole (HxTI) based organic chromophores is developed by structural engineering of the electron donor (D) group in the D–HxTI–benzothiadiazole‐phenyl‐acceptor platform with different fluorenyl moieties, such as unsubstituted fluorenyl (SGT‐146) and hexyloxy (SGT‐147), decyloxy (SGT‐148) and hexyloxy‐phenyl substituted (SGT‐149) fluorenyl moieties. In comparison to a reference dye SGT‐137 with a biphenyl‐based donor, the effects of the donating ability and bulkiness of the fluorenyl based donor in this D–π–A‐structured platform on molecular properties and photovoltaic performance are investigated to establish the structure–property relationship. The photovoltaic performance of dye‐sensitized solar cells (DSSCs) is improved according to the bulkiness of the donor groups. As a result, the DSSCs based on SGT‐149 show high power conversion efficiencies (PCEs) of 11.7% and 10.0% with a [Co(bpy)₃]^2+/3+ (bpy = 2,2′‐bipyridine) and an I⁻/I₃ ⁻ redox electrolyte, respectively. Notably, the co‐sensitization of SGT‐149 with a SGT‐021 porphyrin dye by utilizing a simple “cocktail” method, exhibit state‐of‐the‐art PCEs of 14.2% and 11.6% with a [Co(bpy)₃]^2+/3+ and an I⁻/I₃ ⁻ redox electrolyte, respectively.

A novel benzodithiophene (BDT)‐based small molecule (BDTID‐Cl) is used as an electron donor in small molecules solar cells (SM‐SCs). A record fill factor of 78.0% in SM‐SCs is achieved using BDTID‐Cl as a novel SM donor. In addition, a two‐terminal tandem solar cell is designed with a remarkable power conversion efficiency of 15.1% by complementary absorption of up to 1000 nm.

Abstract

Small molecules have been recently highlighted as active materials owing to their facile synthesisis method, well‐defined molecular structure, and highly reproducible performance. In particular, optimizing bulk heterojunction (BHJ) morphologies is important to achieving high performance in solution‐processable small molecule solar cells (SM‐SCs). Herein, a series of benzodithiophene‐based active materials with different halogen atoms substituted at the end‐group, are reported, as well as how these halogen atoms affect the morphology of BHJ architectures through microstructure analyses. Materials with chlorine atoms show a well‐mixed morphology and interpenetrating networks when blended with [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester, facilitating effective charge transportation. This controlled morphology helps attain excellent performance with a power conversion efficiency (PCE) of 10.5% and a highest fill factor of 78.0% without additives. In addition, it can be applied to two‐terminal (2T)‐tandem solar cells, attaining an outstanding PCE of up to 15.1% with complementary absorption in the field of the 2T‐tandem solar cells introducing the SM‐SCs. These results suggest that tailoring interactions with halogen atoms is an effective way to control BHJ architectures, thereby achieving remarkable performance in SM‐SCs.

A passivation‐conductivity phase‐like diagram enables an organic, conductive passivating contact cell concept and dispels the deep‐seated notion that passivation and conductivity are always in opposition and that Si solar cells must use two materials to achieve interface passivation and carrier transport. The device has the advantages of omitting the use of conventional dielectric passivation materials and simplifying the fabrication process.

Abstract

Defect state passivation and conductivity of materials are always in opposition; thus, it is unlikely for one material to possess both excellent carrier transport and defect state passivation simultaneously. As a result, the use of partial passivation and local contact strategies are required for silicon solar cells, which leads to fabrication processes with technical complexities. Thus, one material that possesses both a good passivation and conductivity is highly desirable in silicon photovoltaic (PV) cells. In this work, a passivation‐conductivity phase‐like diagram is presented and a conductive‐passivating‐carrier‐selective contact is achieved using PEDOT:Nafion composite thin films. A power conversion efficiency of 18.8% is reported for an industrial multicrystalline silicon solar cell with a back PEDOT:Nafion contact, demonstrating a solution‐processed organic passivating contact concept. This concept has the potential advantages of omitting the use of conventional dielectric passivation materials deposited by costly high‐vacuum equipment, energy‐intensive high‐temperature processes, and complex laser opening steps. This work also contributes an effective back‐surface field scheme and a new hole‐selective contact for p‐type and n‐type silicon solar cells, respectively, both for research purposes and as a low‐cost surface engineering strategy for future Si‐based PV technologies.

The effects of the donating ability and bulkiness of the fluorenyl‐based donor in donor–π–acceptor structured organic dyes are investigated to establish the structure–property relationship in terms of molecular properties and photovoltaic performance. Through a simple cock‐tailed co‐sensitization strategy with porphyrin dye, the state‐of‐the‐art efficiencies of 14.2% and 11.6% with cobalt and iodine electrolytes, respectively, are achieved.

Abstract

A new series of 4‐hexyl‐4H‐thieno[3,2‐b]indole (HxTI) based organic chromophores is developed by structural engineering of the electron donor (D) group in the D–HxTI–benzothiadiazole‐phenyl‐acceptor platform with different fluorenyl moieties, such as unsubstituted fluorenyl (SGT‐146) and hexyloxy (SGT‐147), decyloxy (SGT‐148) and hexyloxy‐phenyl substituted (SGT‐149) fluorenyl moieties. In comparison to a reference dye SGT‐137 with a biphenyl‐based donor, the effects of the donating ability and bulkiness of the fluorenyl based donor in this D–π–A‐structured platform on molecular properties and photovoltaic performance are investigated to establish the structure–property relationship. The photovoltaic performance of dye‐sensitized solar cells (DSSCs) is improved according to the bulkiness of the donor groups. As a result, the DSSCs based on SGT‐149 show high power conversion efficiencies (PCEs) of 11.7% and 10.0% with a [Co(bpy)₃]^2+/3+ (bpy = 2,2′‐bipyridine) and an I⁻/I₃ ⁻ redox electrolyte, respectively. Notably, the co‐sensitization of SGT‐149 with a SGT‐021 porphyrin dye by utilizing a simple “cocktail” method, exhibit state‐of‐the‐art PCEs of 14.2% and 11.6% with a [Co(bpy)₃]^2+/3+ and an I⁻/I₃ ⁻ redox electrolyte, respectively.

Side group effect in ternary polymer solar cells is studied by adopting polymers with different side groups. With appropriate side group modification, high power conversion efficiency (PCE) over 13% is realized, which could mainly be attributed to the broadened photoresponse and optimized molecular stacking. The results demonstrate that side group plays a crucial role in determining the molecular stacking of ternary heterojunction.

Abstract

Ternary strategy is a promising approach to broaden the photoresponse of polymer solar cells (PSCs) by adopting combinatory photoactive blends. However, it could lead to a more complicated situation in manipulating the bulk morphology. Achieving an ideal morphology that enhances the charge transport and light absorption simultaneously is an essential avenue to promote the device performance. Herein, two polymers with different lengths of side groups (P1 is based on phenyl side group and P2 is based on biphenyl side group) are adopted in the dual‐acceptor ternary systems to evaluate the relationship between conjugated side group and crystalline behavior in the ternary system. The P1 ternary system delivers a greatly improved power conversion efficiency (PCE) of 13.06%, which could be attributed to the intense and broad photoresponse and improved charge transport originating from the improved crystallinity. Inversely, the P2 ternary device only exhibits a poor PCE of 8.97%, where the decreased device performance could mainly be ascribed to the disturbed molecular stacking of the components originating from the overlong conjugated side group. The results demonstrate a conjugated side group could greatly determine the device performance by tuning the crystallinity of components in ternary systems.

NIR light‐based technique, including optical imaging and photoreglation, has become one of the most important tools for both fundamental research and clinical practice. Herein, the recent progress of NIR light‐based cell function sensing and modulation in cancer theranostics, regenerative medicine, and neuroscience research is summarized.

Abstract

Light‐based technique, including optical imaging and photoregulation, has become one of the most important tools for both fundamental research and clinical practice, such as cell signal sensing, cancer diagnosis, tissue engineering, drug delivery, visual regulation, neuromodulation, and disease treatment. In particular, low energy near‐infrared (NIR, 700–1700 nm) light possesses lower phototoxicity and higher tissue penetration depth in living systems as compared with ultraviolet/visible light, making it a promising tool for in vivo applications. Currently, the NIR light‐based imaging and photoregulation strategies have offered a possibility to real‐time sense and/or modulate specific cellular events in deep tissues with subcellular accuracy. Herein, the recent progress with respect to NIR light for monitoring and modulating the spatiotemporal dynamics of cell functions in living systems are summarized. In particular, the applications of NIR light‐based techniques in cancer theranostics, regenerative medicine, and neuroscience research are systematically introduced and discussed. In addition, the challenges and prospects for NIR light‐based cell sensing and regulating techniques are comprehensively discussed.

The bromination of non‐fullerene acceptors provides a promising alternative approach for the creation of high‐performance organic solar cells. BTIC‐2Br‐m ‐based devices exhibit an outstanding power conversion efficiency of 16.11% with an elevated open circuit voltage of 0.88 V, representing one of the highest efficiencies in brominated non‐fullerene acceptors.

Abstract

The concept of bromination for organic solar cells has received little attention. However, the electron withdrawing ability and noncovalent interactions of bromine are similar to those of fluorine and chlorine atoms. A tetra‐brominated non‐fullerene acceptor, designated as BTIC‐4Br, has been recently developed by introducing bromine atoms onto the end‐capping group of 2‐(3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene) malononitrile and displayed a high power conversion efficiency (PCE) of 12%. To further improve its photovoltaic performance, the acceptor is optimized either by introducing a longer alkyl chain to the core or by modulating the numbers of bromine substituents. After changing each end‐group to a single bromine, the BTIC‐2Br‐m ‐based devices exhibit an outstanding PCE of 16.11% with an elevated open‐circuit voltage of V _oc = 0.88 V, one of the highest PCEs reported among brominated non‐fullerene acceptors. This significant improvement can be attributed to the higher light harvesting efficiency, optimized morphology, and higher exciton quenching efficiencies of the di‐brominated acceptor. These results demonstrate that the substitution of bromine onto the terminal group of non‐fullerene acceptors results in high‐efficiency organic semiconductors, and promotes the use of the halogen‐substituted strategy for polymer solar cell applications.

Herein, presented are various approaches to enhance the outcoupling efficiency of organic light‐emitting diodes (OLEDs) and it is discussed what can be done further to realize their ultimate potential. Then, recent efforts to extend the applications of OLEDs beyond displays are highlighted. As such examples, OLED‐based health‐monitoring sensors, wearable phototherapeutic patches, and fabric‐like OLEDs are introduced.

Abstract

Organic light‐emitting diodes (OLEDs) are established as a mainstream light source for display applications and can now be found in a plethora of consumer electronic devices used daily. This success can be attributed to the rich luminescent properties of organic materials, but efficiency enhancement made over the last few decades has also played a significant role in making OLEDs a practically viable technology. This report summarizes the efforts made so far to improve the external quantum efficiency (EQE) of OLEDs and discusses what should further be done to push toward the ultimate efficiency that can be offered by OLEDs. The study indicates that EQE close to 58% and 80% can be within reach without and with additional light extraction structures, respectively, with an optimal combination of cavity engineering, low‐index transport layers, and horizontal dipole orientation. In addition, recent endeavors to identify possible applications of OLEDs beyond displays are presented with emphasis on their potential in wearable healthcare, such as OLED‐based pulse oximetry as well as phototherapeutic applications based on body‐attachable flexible OLED patches. OLEDs with fabric‐like form factors and washable encapsulation strategies are also introduced as technologies essential to the success of OLED‐based wearable electronics.

Folding‐flexible semitransparent organic solar cells with over 10% efficiency and 21% average visible light transmission are realized by using xylitol microdoping and acid treatment on poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate transparent electrodes for supplying power and promoting plant growth in future multifunctional self‐powered greenhouses.

Abstract

Semitransparent organic solar cells (ST‐OSCs) have attracted extensive attention for their potential greenhouse applications. Conventional ST‐OSCs are typically based on indium tin oxide (ITO) electrodes which suffer from mechanical brittleness. Therefore, alternatives for ITO are required for realization of foldable‐flexible ST‐OSCs (FST‐OSCs). Herein, flexible poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) electrodes are prepared as ITO alternatives via polyhydroxy compound (xylitol) microdoping and acid treatment. As a result, flexible opaque OSCs based on PBDB‐T‐2F:Y6 photoactive system yield a high efficiency of 14.20%. The desirable optical properties of modified PEDOT:PSS electrodes in the visible light region and PBDB‐T‐2F:Y6 photoactive layer in the near‐infrared region facilitate the fabrication of FST‐OSCs with over 10% efficiency and 21% average visible light transmittance. Those FST‐OSCs also display excellent mechanical stability against bending and folding due to the xylitol doping, where over 80% of the initial efficiency can still be maintained even after 1000 folding cycles. Meanwhile, parallel comparisons between plants grown under direct sunlight with a FST‐OSCs roof and those under direct sunlight yield very similar results in terms of branch sturdiness and hypertrophic leaves. The results pave the way for realizing high‐performing FST‐OSCs based on PEDOT:PSS electrodes that could utilize visible light for plant growth and infrared light for power generation.

A novel benzodithiophene (BDT)‐based small molecule (BDTID‐Cl) is used as an electron donor in small molecules solar cells (SM‐SCs). A record fill factor of 78.0% in SM‐SCs is achieved using BDTID‐Cl as a novel SM donor. In addition, a two‐terminal tandem solar cell is designed with a remarkable power conversion efficiency of 15.1% by complementary absorption of up to 1000 nm.

Abstract

Small molecules have been recently highlighted as active materials owing to their facile synthesisis method, well‐defined molecular structure, and highly reproducible performance. In particular, optimizing bulk heterojunction (BHJ) morphologies is important to achieving high performance in solution‐processable small molecule solar cells (SM‐SCs). Herein, a series of benzodithiophene‐based active materials with different halogen atoms substituted at the end‐group, are reported, as well as how these halogen atoms affect the morphology of BHJ architectures through microstructure analyses. Materials with chlorine atoms show a well‐mixed morphology and interpenetrating networks when blended with [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester, facilitating effective charge transportation. This controlled morphology helps attain excellent performance with a power conversion efficiency (PCE) of 10.5% and a highest fill factor of 78.0% without additives. In addition, it can be applied to two‐terminal (2T)‐tandem solar cells, attaining an outstanding PCE of up to 15.1% with complementary absorption in the field of the 2T‐tandem solar cells introducing the SM‐SCs. These results suggest that tailoring interactions with halogen atoms is an effective way to control BHJ architectures, thereby achieving remarkable performance in SM‐SCs.

The effects of the donating ability and bulkiness of the fluorenyl‐based donor in donor–π–acceptor structured organic dyes are investigated to establish the structure–property relationship in terms of molecular properties and photovoltaic performance. Through a simple cock‐tailed co‐sensitization strategy with porphyrin dye, the state‐of‐the‐art efficiencies of 14.2% and 11.6% with cobalt and iodine electrolytes, respectively, are achieved.

Abstract

A new series of 4‐hexyl‐4H‐thieno[3,2‐b]indole (HxTI) based organic chromophores is developed by structural engineering of the electron donor (D) group in the D–HxTI–benzothiadiazole‐phenyl‐acceptor platform with different fluorenyl moieties, such as unsubstituted fluorenyl (SGT‐146) and hexyloxy (SGT‐147), decyloxy (SGT‐148) and hexyloxy‐phenyl substituted (SGT‐149) fluorenyl moieties. In comparison to a reference dye SGT‐137 with a biphenyl‐based donor, the effects of the donating ability and bulkiness of the fluorenyl based donor in this D–π–A‐structured platform on molecular properties and photovoltaic performance are investigated to establish the structure–property relationship. The photovoltaic performance of dye‐sensitized solar cells (DSSCs) is improved according to the bulkiness of the donor groups. As a result, the DSSCs based on SGT‐149 show high power conversion efficiencies (PCEs) of 11.7% and 10.0% with a [Co(bpy)₃]^2+/3+ (bpy = 2,2′‐bipyridine) and an I⁻/I₃ ⁻ redox electrolyte, respectively. Notably, the co‐sensitization of SGT‐149 with a SGT‐021 porphyrin dye by utilizing a simple “cocktail” method, exhibit state‐of‐the‐art PCEs of 14.2% and 11.6% with a [Co(bpy)₃]^2+/3+ and an I⁻/I₃ ⁻ redox electrolyte, respectively.

Fill factor losses in nonfullerene‐acceptor‐based organic solar cells under illumination are caused by morphological traps due to diffusion limited aggregation of the nonfullerene acceptors in the mixed matrix. To achieve stable and high‐performance organic solar cells under illumination, it is essential to engineer the mixed regions from both thin‐film formation kinetics and materials intrinsic properties, e.g., materials compatibility and diffusion constant.

Abstract

As the power conversion efficiency (PCE) of organic solar cells (OSCs) has surpassed the 17% baseline, the long‐term stability of highly efficient OSCs is essential for the practical application of this photovoltaic technology. Here, the photostability and possible degradation mechanisms of three state‐of‐the‐art polymer donors with a commonly used nonfullerene acceptor (NFA), IT‐4F, are investigated. The active‐layer materials show excellent intrinsic photostability. The initial morphology, in particular the mixed region, causes degradation predominantly in the fill factor (FF) under illumination. Electron traps are formed due to the reorganization of polymers and diffusion‐limited aggregation of NFAs to assemble small isolated acceptor domains under illumination. These electron traps lead to losses mainly in FF, which is in contradistinction to the degradation mechanisms observed for fullerene‐based OSCs. Control of the composition of NFAs close to the thermodynamic equilibrium limit while keeping adequate electron percolation and improving the initial polymer and NFA ordering are of the essence to stabilize the FF in NFA‐based solar cells, which may be the key tactics to develop next‐generation OSCs with high efficiency as well as excellent stability.

GABr doping in ideal‐bandgap (≈1.34 eV) Sn–Pb binary perovskite films can efficiently reduce the defect density caused by Sn²⁺ oxidation in the perovskite and reduce the V _OC deficit. As a result, the best PCE of 20.63% with a record small V _OC deficit of 0.33 V is achieved in Sn–Pb binary 1.35 eV PSCs.

Abstract

1.5–1.6 eV bandgap Pb‐based perovskite solar cells (PSCs) with 30–31% theoretical efficiency limit by the Shockley–Queisser model achieve 21–24% power conversion efficiencies (PCEs). However, the best PCEs of reported ideal‐bandgap (1.3–1.4 eV) Sn–Pb PSCs with a higher 33% theoretical efficiency limit are <18%, mainly because of their large open‐circuit voltage (V _oc) deficits (>0.4 V). Herein, it is found that the addition of guanidinium bromide (GABr) can significantly improve the structural and photoelectric characteristics of ideal‐bandgap (≈1.34 eV) Sn–Pb perovskite films. GABr introduced in the perovskite films can efficiently reduce the high defect density caused by Sn²⁺ oxidation in the perovskite, which is favorable for facilitating hole transport, decreasing charge‐carrier recombination, and reducing the V _oc deficit. Therefore, the best PCE of 20.63% with a certificated efficiency of 19.8% is achieved in 1.35 eV PSCs, along with a record small V _oc deficit of 0.33 V, which is the highest PCE among all values reported to date for ideal‐bandgap Sn–Pb PSCs. Moreover, the GABr‐modified PSCs exhibit significantly improved environmental and thermal stability. This work represents a noteworthy step toward the fabrication of efficient and stable ideal‐bandgap PSCs.

Nature Photonics, Published online: 24 February 2020; doi:10.1038/s41566-020-0593-1

A luminescent photonic substrate with a controlled angular emission profile is introduced and its ability to generate high-contrast dark-field images of micrometre-sized living organisms is demonstrated using standard optical microscopy equipment.

Graphitic carbon nitride (g‐C₃N₄) is doped into PEDOT:PSS to improve the conductivity by weakening the shield effect of PSS on conductive PEDOT. Employing g‐C₃N₄ doped PEDOT:PSS as a hole transport layer for PM6:Y6‐based organic solar cells, a device efficiency of up to 16.4% is achieved, partly as a result of improved charge transport and suppressed charge recombination at the interface.

Abstract

The power‐conversion efficiency (PCE) of single‐junction organic solar cells (OSCs) has exceeded 16% thanks to the development of non‐fullerene acceptor materials and morphological optimization of active layer. In addition, interfacial engineering always plays a crucial role in further improving the performance of OSCs based on a well‐established active‐layer system. Doping of graphitic carbon nitride (g‐C₃N₄) into poly(3,4‐ethylene‐dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a hole transport layer (HTL) for PM6:Y6‐based OSCs is reported, boosting the PCE to almost 16.4%. After being added into the PEDOT:PSS, the g‐C₃N₄ as a Bronsted base can be protonated, weakening the shield effect of insulating PSS on conductive PEDOT, which enables exposures of more PEDOT chains on the surface of PEDOT:PSS core‐shell structure, and thus increasing the conductivity. Therefore, at the interface between g‐C₃N₄ doped HTL and PM6:Y6 layer, the charge transport is improved and the charge recombination is suppressed, leading to the increases of fill factor and short‐circuit current density of devices. This work demonstrates that doping g‐C₃N₄ into PEDOT:PSS is an efficient strategy to increase the conductivity of HTL, resulting in higher OSC performance.

The vast majority of ternary organic solar cells are obtained by simply fabricating bulk heterojunction active layers. Herein, a new method by fabricating pseudoplanar heterojunction ternary organic solar cells is proposed. At the same time, the alloyed acceptor is likely formed between two nonfullerene acceptors, which may be more suitable for facilitating pseudoplanar heterojunctions.

Abstract

The vast majority of ternary organic solar cells are obtained by simply fabricating bulk heterojunction (BHJ) active layers. Due to the inappropriate distribution of donors and acceptors in the vertical direction, a new method by fabricating pseudoplanar heterojunction (PPHJ) ternary organic solar cells is proposed to better modulate the morphology of active layer. The pseudoplanar heterojunction ternary organic solar cells (P‐ternary) are fabricated by a sequential solution treatment technique, in which the donor and acceptor mixture blends are sequentially spin‐coated. As a consequence, a higher power conversion efficiency (PCE) of 14.2% is achieved with a V _oc of 0.79 V, J _sc of 25.6 mA cm⁻², and fill factor (FF) of 69.8% compared with the ternary BHJ system of 13.8%. At the same time, the alloyed acceptor is likely formed between two the acceptors through a series of in‐depth explorations. This work suggests that nonfullerene alloyed acceptor may have great potential to realize effective P‐ternary organic solar cells.

Herein, 17% efficient and stable ternary organic solar cells are realized by introducing a delayed fluorescence material 3,4‐bis(4‐(diphenylamino)phenyl)acenaphtho[1,2‐b]pyrazine‐8,9‐dicarbonitrile (APDC‐TPDA) in a non‐fullerene system. Long‐lifetime singlet excitons on APDC‐TPDA can transfer to the polymer donor to prolong the excitons lifetime and suppress the reverse energy transfer from charge transfer state to triplet state, and then reduce the recombination energy loss of the device.

Abstract

Charge transfer state (CT) plays an important role in exciton diffusion, dissociation, and charge recombination mechanisms. Enhancing the utilization and suppressing the recombination process of CT excitons is a promising way to improve the performance of organic solar cells (OSCs). Here, an effective method is presented via introducing a delayed fluorescence (DF) emitter 3,4‐bis(4‐(diphenylamino)phenyl)acenaphtho[1,2‐b]pyrazine‐8,9‐dicarbonitrile (APDC‐TPDA) in OSCs. The long‐lifetime singlet excitons on APDC‐TPDA can transfer to polymer donors to prolong exciton lifetime, which ensures sufficient time for diffusion and dissociation. Concurrently, the high triplet energy level (T₁) of the DF material can also prevent the reverse energy transfer from CT to T₁. APDC‐TPDA‐containing ternary OSCs shows a high PCE of 16.96% with a reduced recombination energy loss of 0.46 eV. It is noteworthy that the ternary OSC also exhibits superior storage stability. After 55 days of storage, the PCE of the ternary OSC still retains about 96% of its primitive state. Furthermore, this ternary strategy is efficient and universally applicable to OSCs, and positive results can be obtained in different systems with different DF emitters. These results indicate that the ternary strategy provides a new design idea to realize high performance OSCs.

Polymer aggregation and miscibility have been demonstrated to influence photovoltaic performance in nonfullerene‐based organic solar cells. Polymers having a strong tendency to aggregate are herein found to undergo aggregation prior to liquid–liquid phase separation and have a higher miscibility with nonfullerene acceptors, resulting in mixed donor–acceptor domains, stronger PL quenching, and a higher exciton dissociation efficiency.

Abstract

Understanding the correlation between polymer aggregation, miscibility, and device performance is important to establish a set of chemistry design rules for donor polymers with nonfullerene acceptors (NFAs). Employing a donor polymer with strong temperature‐dependent aggregation, namely PffBT4T‐2OD [poly[(5,6‐difluoro‐2,1,3‐benzothiadiazol‐4,7‐diyl)‐alt‐(3,3″′‐di(2‐octyldodecyl)‐2,2′;5′,2″;5″,2″′‐quaterthiophen‐5,5‐diyl)], also known as PCE‐11 as a base polymer, five copolymer derivatives having a different thiophene linker composition are blended with the common NFA O‐IDTBR to investigate their photovoltaic performance. While the donor polymers have similar optoelectronic properties, it is found that the device power conversion efficiency changes drastically from 1.8% to 8.7% as a function of thiophene content in the donor polymer. Results of structural characterization show that polymer aggregation and miscibility with O‐IDTBR are a strong function of the chemical composition, leading to different donor–acceptor blend morphology. Polymers having a strong tendency to aggregate are found to undergo fast aggregation prior to liquid–liquid phase separation and have a higher miscibility with NFA. These properties result in smaller mixed donor–acceptor domains, stronger PL quenching, and more efficient exciton dissociation in the resulting cells. This work indicates the importance of both polymer aggregation and donor–acceptor interaction on the formation of bulk heterojunctions in polymer:NFA blends.

Publication date: April 2020

Source: Materials Science and Engineering: R: Reports, Volume 140

Author(s): Shumeng Wang, Hongyang Zhang, Baohua Zhang, Zhiyuan Xie, Wai-Yeung Wong