Yingzhi Jin

The surface functionalization of 2D materials is critical for tuning properties and application performance. In the case of MXenes, oxygen‐terminated surfaces are critical for applications in energy storage and catalysis. Here, a route for exclusively functionalizing MXene surfaced by oxygen is shown and pushed to the limit.

Abstract

Tuning and tailoring of surface terminating functional species hold the key to unlock unprecedented properties for a wide range of applications of the largest 2D family known as MXenes. However, a few routes for surface tailoring are explored and little is known about the extent to which the terminating species can saturate the MXene surfaces. Among available terminations, atomic oxygen is of interest for electrochemical energy storage, hydrogen evolution reaction, photocatalysis, etc. However, controlled oxidation of the surfaces is not trivial due to the favored formation of oxides. In the present contribution, single sheets of Ti₃C₂T _x MXene, inherently terminated by F and O, are defluorinated by heating in vacuum and subsequentially exposed to O₂ gas at temperatures up to 450 °C in situ, in an environmental transmission electron microscope. Results include exclusive termination by O on the MXene surfaces and eventual supersaturation (x > 2) with a retained MXene sheet structure. Upon extended O exposure, the MXene structure transforms into TiO₂ and desorbs surface bound H₂O and CO₂ reaction products. These results are fundamental for understanding the oxidation, the presence of water on MXene surfaces, and the degradation of MXenes, and pave way for further tailoring of MXene surfaces.

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 layer-by-layer (LbL) strategy exhibits unique advantages of combining the merits of high photo-absorption rate, suitable vertical phase separation, and good practicability, endowing the LbL-bladed devices with a higher power conversion efficiency (PCE) of 16.35% compared to the bulk heterojunction (BHJ)-bladed device (15.37%). Importantly, this LbL approach can effectively reduce the scaling lag of module efficiency. An LbL-bladed solar module with a geometrical fill factor of over 90% exhibited an outstanding PCE of 11.86%.

A dynamic energy model is used to demonstrate that semitransparent organic solar cells (OSCs) can be employed on greenhouses to achieve net zero energy greenhouses in warm and moderate climates. Furthermore, it is shown that the reduction in sunlight entering the greenhouses is not as significant as the transmittance of the OSCs would suggest owing in part to the OSCs replacing the need for shade-cloths. These results demonstrate the significant opportunity of OSC-greenhouses for high-yield, environmentally friendly agriculture.

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.

Color‐selective organic photodiodes are inkjet printed using a novel photoactive material system based on nonfullerene acceptors. This material system simplifies process development and at the same time enables a high degree of color tunability. Energetic and morphological properties are investigated and the color‐selective devices are employed in a multichannel visible‐light‐communication system.

Abstract

Future lightweight, flexible, and wearable electronics will employ visible‐light‐communication schemes to interact within indoor environments. Organic photodiodes are particularly well suited for such technologies as they enable chemically tailored optoelectronic performance and fabrication by printing techniques on thin and flexible substrates. However, previous methods have failed to address versatile functionality regarding wavelength selectivity without increasing fabrication complexity. This work introduces a general solution for printing wavelength‐selective bulk‐heterojunction photodetectors through engineering of the ink formulation. Nonfullerene acceptors are incorporated in a transparent polymer donor matrix to narrow and tune the response in the visible range without optical filters or light‐management techniques. This approach effectively decouples the optical response from the viscoelastic ink properties, simplifying process development. A thorough morphological and spectroscopic investigation finds excellent charge‐carrier dynamics enabling state‐of‐the‐art responsivities >10² mA W⁻¹ and cutoff frequencies >1.5 MHz. Finally, the color selectivity and high performance are demonstrated in a filterless visible‐light‐communication system capable of demultiplexing intermixed optical signals.

A novel sidechain‐modified 3,4‐ethylene dioxythiophene derivative is polymerized in a large‐area roll‐to‐roll process. As an electrochromic thin film, the corresponding poly(3,4‐ethylene dioxythiophene) derivative shows enhanced electrochromic properties regarding visible light transmittance change (Δτ _v = 59%, ΔL* = 54.1), coloration efficiency (η = 530 cm² C⁻¹) and color neutrality in the bleached state (L* = 83.8, a* = −4.3, b* = −4.1).

Abstract

Conjugated electrochromic (EC) polymers for flexible EC devices (ECDs) generally lack a fully colorless bleached state. A strategy to overcome this drawback is the implementation of a new sidechain‐modified poly(3,4‐ethylene dioxythiophene) derivative that can be deposited in thin‐film form in a customized high‐throughput and large‐area roll‐to‐roll polymerization process. The sidechain modification provides enhanced EC properties in terms of visible light transmittance change, Δτ_v = 59% (ΔL* = 54.1), contrast ratio (CR = 15.8), coloration efficiency (η = 530 cm² C⁻¹), and color neutrality (L* = 83.8, a* = −4.3, b* = −4.1) in the bleached state. The intense blue‐colored polymer thin films exhibit high cycle stability (10 000 cycles) and fast response times. The design, synthesis, and polymerization of the modified 3,4‐ethylene dioxythiophene derivative are discussed along with a detailed optical, electrochemical, and spectroelectrochemical characterization of the resulting EC thin films. Finally, a flexible see‐through ECD with a visible light transmittance change of Δτ_v = 47% (ΔL* = 51.9) and a neutral‐colored bleached state is developed.

A novel benzo[1,2‐b:4,5‐b′]difuran (BDF)‐based copolymer, L2, is designed and synthesized. When blended with a non‐fullerene small molecule acceptor TTPT‐T‐4F, the L2‐based device exhibits an efficiency of 14.0%, which is higher than that (12.72%) of its analogue benzo[1,2‐b:4,5‐b′]dithiophene (BDT) copolymer‐based device. Thus, the performance of the BDF‐based copolymers are equal to or greater than that of the BDT‐based counterparts.

Abstract

The development of high‐performance donor polymers is important for obtaining high power conversion efficiencies (PCEs) of non‐fullerene polymer solar cells (PSCs). Currently, most high‐efficiency PSCs are fabricated with benzo[1,2‐b:4,5‐b′]dithiophene (BDT)‐based conjugated polymers. The photovoltaic performance of benzo[1,2‐b:4,5‐b′]difuran (BDF)‐based copolymers has lagged far behind that of BDT‐based counterparts. In this study, a novel BDF‐based copolymer L2 is designed and synthesized, in which BDF and benzotriazole (BTz) building blocks have been used as the electron‐sufficient and deficient units, respectively. When blending with a non‐fullerene small molecule acceptor (SMA), TTPT‐T‐4F, the L2‐based device exhibits a remarkably high PCE of 14.0%, which is higher than that of the device fabricated by its analogue BDT copolymer (12.72%). Moreover, PSCs based on the L2:TTPT‐T‐4F blend demonstrate excellent ambient stability with 92% of its original PCE remaining after storage in air for 1800 h. Thus, BDF is a promising electron‐donating unit, and the BDF‐based copolymers can be competitive or even surpass the performance of BDT‐based counterparts.

A highly efficient organic solar cell is demonstrated by applying a chlorine‐functionalized graphdiyne (GCl) multifunctional solid additive. A record‐high efficiency of 17.3%, with certified efficiency of 17.1%, is obtained along with the simultaneous increase of short‐circuit current (J _sc) and fill factor (FF), displaying state‐of‐the‐art binary organic solar cells at present.

Abstract

Morphology tuning of the blend film in organic solar cells (OSCs) is a key approach to improve device efficiencies. Among various strategies, solid additive is proposed as a simple and new way to enable morphology tuning. However, there exist few solid additives reported to meet such expectations. Herein, chlorine‐functionalized graphdiyne (GCl) is successfully applied as a multifunctional solid additive to fine‐tune the morphology and improve device efficiency as well as reproductivity for the first time. Compared with 15.6% efficiency for control devices, a record high efficiency of 17.3% with the certified one of 17.1% is obtained along with the simultaneous increase of short‐circuit current (J _sc) and fill factor (FF), displaying the state‐of‐the‐art binary organic solar cells at present. The redshift of the film absorption, enhanced crystallinity, prominent phase separation, improved mobility, and decreased charge recombination synergistically account for the increase of J _sc and FF after introducing GCl into the blend film. Moreover, the addition of GCl dramatically reduces batch‐to‐batch variations benefiting mass production owing to the nonvolatile property of GCl. All these results confirm the efficacy of GCl to enhance device performance, demonstrating a promising application of GCl as a multifunctional solid additive in the field of OSCs.

The significant advances in chlorinated photovoltaic materials have boosted the performances of organic solar cells (OSCs) from 4% to 17% only in 7 years. The design approaches utilizing chlorination as an effective tool to achieve high performance in OSCs are summarized. Furthermore, future challenges and prospects of these materials to realize the successful commercialization of OSCs are presented.

Abstract

The pursuit of low‐cost, flexible, and lightweight renewable power resources has led to outstanding advancements in organic solar cells (OSCs). Among the successful design principles developed for synthesizing efficient conjugated electron donor (ED) or acceptor (EA) units for OSCs, chlorination has recently emerged as a reliable approach, despite being neglected over the years. In fact, several recent studies have indicated that chlorination is more potent for large‐scale production than the highly studied fluorination in several aspects, such as easy and low‐cost synthesis of materials, lowering energy levels, easy tuning of molecular orientation, and morphology, thus realizing impressive power conversion efficiencies in OSCs up to 17%. Herein, an up‐to‐date summary of the current progress in photovoltaic results realized by incorporating a chlorinated ED or EA into OSCs is presented to recognize the benefits and drawbacks of this interesting substituent in photoactive materials. Furthermore, other aspects of chlorinated materials for application in all‐small‐molecule, semitransparent, tandem, ternary, single‐component, and indoor OSCs are also presented. Consequently, a concise outlook is provided for future design and development of chlorinated ED or EA units, which will facilitate utilization of this approach to achieve the goal of low‐cost and large‐area OSCs.

Ultrahigh UV‐sensitive organic phototransistors are constructed based on two new distriphenylamineethynylpyrene derivatives developed in this research, which demonstrate outstanding photoelectrical performances with photoresponsivity of 2.86 × 10⁶ A W⁻¹ and detectivity of approaching 1.49 × 10¹⁸ Jones due to their good integration of efficient charge transport, optical property, and small exciton binding energies in the small molecule.

Abstract

Organic photodetectors with UV‐sensitivity are of great potential for various optoelectronic applications. Integration of high charge carrier mobility, long exciton diffusion length as well as unique UV‐sensitivity for active materials is crucial for construction of UV‐sensitive devices with high performance, however, very few organic semiconductors can integrate these properties simultaneously. Herein, two novel organic semiconductors containing large steric hindrance triphenylamine groups, 1,6‐distriphenylamineethynylpyrene (1,6‐DTEP) and 2,7‐distriphenylamineethynylpyrene (2,7‐DTEP) are designed and synthesized. It demonstrates that the single crystals of both 1,6‐DTEP and 2,7‐DTEP exhibit superior integrated optoelectronic properties of high charge carrier mobility, unique UV absorption, high photoluminescence quantum yields as well as small exciton binding energies. Organic phototransistors constructed using 1,6‐DTEP and 2,7‐DTEP single crystals show ultrasensitive performance with ultra‐high photoresponsivity of 2.86 × 10⁶ and 1.04 × 10⁵ A W⁻¹, detectivity (D*) of above 1.49 × 10¹⁸ and 5.28 × 10¹⁶ Jones under 370 nm light illumination, respectively. It indicates the great potential of 1,6‐DTEP and 2,7‐DTEP‐based phototransistors for organic UV‐photodetector applications and also provides a new design strategy to develop series of better performance UV photoelectric organic materials for related research in organic optoelectronics.

A highly efficient organic solar cell is demonstrated by applying a chlorine‐functionalized graphdiyne (GCl) multifunctional solid additive. A record‐high efficiency of 17.3%, with certified efficiency of 17.1%, is obtained along with the simultaneous increase of short‐circuit current (J _sc) and fill factor (FF), displaying state‐of‐the‐art binary organic solar cells at present.

Abstract

Morphology tuning of the blend film in organic solar cells (OSCs) is a key approach to improve device efficiencies. Among various strategies, solid additive is proposed as a simple and new way to enable morphology tuning. However, there exist few solid additives reported to meet such expectations. Herein, chlorine‐functionalized graphdiyne (GCl) is successfully applied as a multifunctional solid additive to fine‐tune the morphology and improve device efficiency as well as reproductivity for the first time. Compared with 15.6% efficiency for control devices, a record high efficiency of 17.3% with the certified one of 17.1% is obtained along with the simultaneous increase of short‐circuit current (J _sc) and fill factor (FF), displaying the state‐of‐the‐art binary organic solar cells at present. The redshift of the film absorption, enhanced crystallinity, prominent phase separation, improved mobility, and decreased charge recombination synergistically account for the increase of J _sc and FF after introducing GCl into the blend film. Moreover, the addition of GCl dramatically reduces batch‐to‐batch variations benefiting mass production owing to the nonvolatile property of GCl. All these results confirm the efficacy of GCl to enhance device performance, demonstrating a promising application of GCl as a multifunctional solid additive in the field of OSCs.