Yingzhi Jin

Alternating copolymers of fluorene and azobenzene exhibit exceptional chiroptical properties in annealed thin films. The chiroptical properties, polymer chain alignment, and their supramolecular helicity can be fully controlled by irradiating with polarized light. Intriguingly, the diastereomeric relationship between the supramolecular helicity of polymer and the circular polarization of light leads to an asymmetric helix inversion pathway, reminiscent of molecular motors.

Abstract

Control over main‐chain motion of chiral π‐conjugated polymers can lead to unexpected new functionalities. Here, it is shown that by combining photoswitchable azobenzene units in conjugation with chiral fluorene comonomers and appropriate plasticizers, the polymer organization and chiroptical properties of these alternating copolymers steered by light and its state of polarization can be dynamically controlled. The configuration of the stereogenic centers in the side chains of the fluorene units determines the handedness of the cholesteric organization in thermally annealed films, indicating cooperative behavior. The polymer alignment and helicity of the supramolecular arrangement can be switched by irradiating with linearly and circularly polarized light, respectively. Intriguingly, when switching the handedness of thermally induced cholesteric organizations by illuminating with circularly polarized light that is opposite to the handedness of the cholesteric phases, a nematic‐like intermediate state is observed during helix interconversion. By the sequence of irradiation with left and right circularly polarized light followed by thermal annealing, an asymmetric motion, reminiscent of that seen in molecular motors is observed. These findings suggest that functional conjugated polymers can exhibit emergent properties at mesoscopic scale.

Self‐assembled multi‐iodinated boron dipyrromethene micelles (IBMs), via the interplay of both π–π stacking and hydrophobic interactions, are reported. These IBMs cause efficient cascade delivery into cytoplasm and tunable photoconversion for yielding potent antitumor synergy against triple‐negative breast cancer together with distinctly reduced recurrence and metastasis through the reversal of tumor immunosuppression.

Abstract

Triple‐negative breast cancer (TNBC) remains with highest incidence and mortality rates among females, and a critical bottleneck lies in rationally establishing potent therapeutics against TNBC. Here, the self‐assembled micellar nanoarchitecture of heavy‐atom‐modulated supramolecules with efficient cytoplasmic translocation and tunable photoconversion is shown, for potent suppression against primary, metastatic, and recurrent TNBC. Multi‐iodinated boron dipyrromethene micelles yield tunable photoconversion into singlet oxygen and a thermal effect, together with deep penetration and subsequent cytoplasmic translocation at the tumor. Tetra‐iodinated boron dipyrromethene micelles (4‐IBMs) particularly show a distinctly enhanced cooperativity of antitumor efficiency through considerable expressions of apoptotic proteins, potently suppressing subcutaneous, and orthotopic TNBC models, together with reduced oxygen dependence. Furthermore, 4‐IBMs yield preferable anti‐metastatic and anti‐recurrent efficacies through the inhibition of metastasis‐relevant proteins, distinct immunogenic cell death, and re‐education of M2 macrophages into tumoricidal M1 phenotype as compared to chemotherapy and surgical resection. These results offer insights into the cooperativity of supramolecular nanoarchitectures for potent phototherapy against TNBC.

The recent progress in potentially low‐cost polythiophene:nonfullerene‐based solar cells is reviewed from the viewpoints of molecular engineering and morphology control. The molecular design strategies of polythiophenes and nonfullerene acceptors are discussed, followed by the recent achievements in understanding and controlling the morphology of polythiophene:nonfullerene blends. Finally, the future challenges are delineated for advancing the commercial applications of polythiophenes in solar cells.

Abstract

With the advances in organic photovoltaics (OPVs), the development of low‐cost and easily accessible polymer donors is of vital importance for OPV commercialization. Polythiophene (PT) and its derivatives stand out as the most promising members of the photovoltaic material family for commercial applications, owing to their low cost and high scalability of synthesis. In recent years, PTs, paired with nonfullerene acceptors, have progressed rapidly in photovoltaic performance. This Review gives an overview of the strategies in designing PTs for nonfullerene OPVs from the perspective of energy level modulation. A survey of the typical classes of nonfullerene acceptors designed for pairing with the benchmark PT, i.e., poly(3‐hexylthiophene) (P3HT) is also presented. Furthermore, recent achievements in understanding and controlling the film morphology for PT:nonfullerene blends are discussed in depth. In addition to the effects of molecular weight and blend ratio on film morphology, the crucial roles of miscibility between PT and nonfullerene and processing solvent in determining film microstructure and morphology are highlighted, followed by a discussion on thermal annealing and ternary active layers. Finally, the remaining questions and the prospects of the low‐cost PT:nonfullerene systems are outlined. It is hoped that this review can guide the optimization of PT:nonfullerene blends and advance their commercial applications.

A rational interface engineering strategy is presented for the potassium‐guided grain growth of deep‐blue perovskites with controlled crystal orientation. Efficient and stable perovskite LEDs emitting at 469 nm exhibit an external quantum efficiency of 4.14% and a Commission Internationale de l'Eclairage coordinate of (0.125, 0.076), matching well the National Television System Committee (NTSC) standard blue.

Abstract

Perovskite light‐emitting diodes (PeLEDs) are emerging candidates for the applications of solution‐processed full‐color displays. However, the device performance of deep‐blue PeLED still lags far behind that of their red and green counterparts, which is largely limited by low external quantum efficiency (EQE) and poor operational stability. Here, a facile and reliable crystallization strategy for perovskite grains is proposed, with improved deep‐blue emission through rational interfacial engineering. By modifying the substrate with potassium cation (K⁺) as the supplier of heterogeneous nucleation seeds, the interfacial K⁺‐guided grain growth is realized for well‐packed perovskite assemblies with high surface coverage and the controlled crystal orientation, leading to the enhanced radiative recombination and hole‐transport capabilities. Synergistical boost in device performance is achieved for deep‐blue PeLEDs emitting at 469 nm with a peak EQE of 4.14%, a maximum luminance of 451 cd m^–2, and spectrally stable color coordinates of (0.125, 0.076) that matches well with the National Television System Committee (NTSC) standard blue.

Using time‐resolved time‐of‐flight secondary ion mass spectrometry, electric field and light induced ion migration in hybrid organic‐inorganic perovskites are directly observed, revealing the migration behavior of methylammonium and halides. It is found that light‐induced methylammonium migration is more significant. In addition, the light with sub‐bandgap energy cannot induce ion migration.

Abstract

Unique optoelectronic, electronic, and sensing properties of hybrid organic–inorganic perovskites (HOIPs) are underpinned by the complex interactions between electronic and ionic states. Here, the photoinduced field ion migration in HOIPs is directly observed. Using newly developed local probe time‐resolved techniques, more significant CH₃NH₃ ⁺ migration than I⁻/Br⁻ migration in HOIPs is unveiled. It is found that light illumination only induces CH₃NH₃ ⁺ migration but not I⁻/Br⁻ migration. By directly observing temporal changes in bias‐induced and photoinduced ion migration in device conditions, it is revealed that light illumination suppresses the bias‐induced ion redistribution in the lateral device. These findings, being a necessary compensation of previous understandings of ion migration in HOIPs based on simulations and static and/or indirect measurements, offer advanced insights into the distinct light effects on the migration of organic cation and halides in HOIPs, which are expected to be helpful for improving the performance and the long‐term stability of HOIPs optoelectronics.

9.5% semitransparent solar cells with ultrahigh transmission in the visible range (50% AVT) are fabricated via inkjet printing. The effect of different photoactive layer ink solvents on the vertical stratification and performance is explored. The formulation of transport layer inks compatible with highly hydrophobic active layers and with scalable printing processes permits the use of a semitransparent electrode grid.

Abstract

New polymer donors and nonfullerene acceptors have elevated the performance and stability of solar cells to higher grounds. To achieve their full potential, they require their adaptation to scalable and cost‐effective solution manufacturing techniques for large area deposition. Likewise, formulating scalable solution‐based transport layer inks that are compatible with the photoactive layer is imperative. This manuscript reports the full integration of solution‐based transport layers and electrode alongside a PTB7‐Th:IEICO‐4F bulk heterojunction in inverted architecture through inkjet‐printing, resulting in power conversion efficiencies up to 12.4% opaque devices and 9.5% semitransparent devices with average visible transmittance values of 50.1%, including hole transport layer. The wetting envelope of the highly‐hydrophobic photoactive layer alongside the surface energy of candidate solutions and solvents allows the formulation of thick transport layer inks that are compatible with the drop‐on‐demand inkjet‐printing process and yield uniform and homogenous films. Moreover, the surface energy components of the donor and acceptor serves as a fingerprint to assess the vertical stratification of the photoactive layer with the inclusion of different solvents. This methodology addresses a scale‐up bottleneck of solution‐based transport layers for high‐efficiency organic cells, enabling its adaptation to high‐throughput techniques including slot‐die and roll‐to‐roll coating.

A highly crystalline poly(3, 4‐ethylenedioxythiophene) (PEDOT) nanofiber prepared by using a highly crystalline nanocellulose extracted from Cladophora algae as a bio‐based template. The resultant PEDOT nanofibers not only possess high electrical conductivity, but also possess exciting reprocessability, and can be assembled into bulk functional materials of various dimensions including 1D microfibers, 2D nanopapers and 3D aerogels.

Abstract

Packing conjugated conducting polymer chains into long‐range order can significantly boost their carrier‐transport properties, allowing the design and enhancing the performance of applications in next‐generation flexible electronics, energy storage, etc. However, strategies for organizing molecular chains have hitherto been challenging and have been associated with poor reprocessability. This paper discusses the development and application of highly crystalline poly(3, 4‐ethylenedioxythiophene) (PEDOT) nanofibers. These highly conductive PEDOT nanofibers possess well‐defined quasi‐one‐dimensional topology combined with highly ordered molecular chain arrangements as a result of interface‐induced morphological shaping followed by recrystallization induced by Cladophora cellulose. The nanofibers are also easily dispersible and able to be reprocessed in aqueous solution. The multiple functionalities of these PEDOT nanofibers are demonstrated by using them as building blocks for applications such as 1D assembled microfibers in an ultra‐sensitive strain sensor, 2D papers for electrochemical energy storage, and 3D aerogels for simultaneous solar‐thermal distillation and thermoelectricity generation. The methods discussed here can be the basis of a new avenue for regulating the molecular structure of, processing, and discovering applications for conjugated conducting polymers.

An electrochromic polymer enables rapid and facile bacterial detection and susceptibility evaluation. The reducing species (e.g., cysteine and glutathione) released by metabolically active bacteria induce spectroscopic and colorimetric change of the polymer.

Abstract

The electrochromism of a water‐soluble naturally oxidized electrochromic polymer, ox‐PPE, is harnessed for rapid and facile bacterial detection, discrimination, and susceptibility testing. The ox‐PPE solution shows distinct colorimetric and spectroscopic changes within 30 min when mixed with live bacteria. For the underlying mechanism, it is found that ox‐PPE responds to the reducing species (e.g., cysteine and glutathione) released by metabolically active bacteria. This reduction reaction is ubiquitous among various bacterial strains, with a noticeable difference that enables discrimination of Gram‐negative and Gram‐positive bacterial strains. Combining ox‐PPE with antibiotics, methicillin‐susceptible and methicillin‐resistant Staphylococcus aureus can be differentiated within 2.5 h. Proof‐of‐concept demonstration of ox‐PPE for antimicrobial susceptibility testing is carried out by incubating Escherichia coli with various antibiotics. The obtained minimum inhibition concentrations are consistent with the conventional culture‐based methods, but with the procedure time significantly shortened to 3 h.

The photogeneration pathways in two non‐fullerene acceptor solar cells are investigated using charge extraction measurements. They reveal higher photogeneration yield and weaker electric field dependence for the nonrelaxed charge transfer states in PTB7‐Th:ITIC. The low molecular quadrupole moment of h‐ITIC, the dipolar analogue of ITIC, reduces delocalization of electron–hole pairs at the donor–acceptor interface lowering the yield.

Abstract

In organic solar cells, photogenerated singlet excitons form charge transfer (CT) complexes, which subsequently split into free charge carriers. Here, the contributions of excess energy and molecular quadrupole moments to the charge separation process are considered. The charge photogeneration in two separate bulk heterojunction systems consisting of the polymer donor PTB7‐Th and two non‐fullerene acceptors, ITIC and h‐ITIC, is investigated. CT state dissociation in these donor–acceptor systems is monitored by charge density decay dynamics obtained from transient absorption experiments. The electric field dependence of charge carrier generation is studied at different excitation energies by time delayed collection field (TDCF) and sensitive steady‐state photocurrent measurements. Upon excitation below the optical gap, free charge carrier generation becomes less field dependent with increasing photon energy, which challenges the view of charge photogeneration proceeding through energetically lowest CT states. The average distance between electron–hole pairs at the donor–acceptor interface is determined from empirical fits to the TDCF data. The delocalization of CT states is larger in PTB7‐Th:ITIC, the system with larger molecular quadrupole moment, indicating the sizeable effect of the electrostatic potential at the donor–acceptor interface on the dissociation of CT complexes.

Although beneficial to ion transport, swelling can affect the performance and durability of organic mixed conductor devices. A hydrophilic conjugated polymer, poly[3‐(6‐hydroxy)hexylthiophene] is presented, and its swelling properties are compared to state‐of‐the‐art glycolated organic semiconductors for bioelectronics. Hydroxyl functionalization of poly(thiophene) backbone minimizes swelling while still allowing good ion uptake, resulting in robust organic electrochemical transistor operation in aqueous electrolytes.

Abstract

Organic mixed conductors find use in batteries, bioelectronics technologies, neuromorphic computing, and sensing. While great progress has been achieved, polymer‐based mixed conductors frequently experience significant volumetric changes during ion uptake/rejection, i.e., during doping/de‐doping and charging/discharging. Although ion dynamics may be enhanced in expanded networks, these volumetric changes can have undesirable consequences, e.g., negatively affecting hole/electron conduction and severely shortening device lifetime. Here, the authors present a new material poly[3‐(6‐hydroxy)hexylthiophene] (P3HHT) that is able to transport ions and electrons/holes, as tested in electrochemical absorption spectroscopy and organic electrochemical transistors, and that exhibits low swelling, attributed to the hydroxylated alkyl side‐chain functionalization. P3HHT displays a thickness change upon passive swelling of only +2.5%, compared to +90% observed for the ubiquitous poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate, and +10 to +15% for polymers such as poly(2‐(3,3′‐bis(2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy)‐[2,2′‐bithiophen]‐5‐yl)thieno[3,2‐b]thiophene) (p[g2T‐TT]). Applying a bias pulse during swelling, this discrepancy becomes even more pronounced, with the thickness of P3HHT films changing by <10% while that of p(g2T‐TT) structures increases by +75 to +80%. Importantly, the initial P3HHT film thickness is essentially restored after de‐doping while p(g2T‐TT) remains substantially swollen. The authors, thus, expand the materials‐design toolbox for the creation of low‐swelling soft mixed conductors with tailored properties and applications in bioelectronics and beyond.

Two well‐regular polymer acceptors (PY‐IT and PY‐OT) with different polymerization sites are developed. For comparison, a random ternary copolymer (PY‐IOT) with the same ratio of the two acceptors is synthesized. All‐polymer solar cells (PSCs) based on PM6:PY‐IT achieve an excellent PCE of 15.05%, which is significantly higher than those based on PY‐OT (10.04%) and PY‐IOT (12.12%).

Abstract

Recent advances in the development of polymerized A–D–A‐type small‐molecule acceptors (SMAs) have promoted the power conversion efficiency (PCE) of all‐polymer solar cells (all‐PSCs) over 13%. However, the monomer of an SMA typically consists of a mixture of three isomers due to the regio‐isomeric brominated end groups (IC‐Br(in) and IC‐Br(out)). In this work, the two isomeric end groups are successfully separated, the regioisomeric issue is solved, and three polymer acceptors, named PY‐IT, PY‐OT, and PY‐IOT, are developed, where PY‐IOT is a random terpolymer with the same ratio of the two acceptors. Interestingly, from PY‐OT, PY‐IOT to PY‐IT, the absorption edge gradually redshifts and electron mobility progressively increases. Theory calculation indicates that the LUMOs are distributed on the entire molecular backbone of PY‐IT, contributing to the enhanced electron transport. Consequently, the PM6:PY‐IT system achieves an excellent PCE of 15.05%, significantly higher than those for PY‐OT (10.04%) and PY‐IOT (12.12%). Morphological and device characterization reveals that the highest PCE for the PY‐IT‐based device is the fruit of enhanced absorption, more balanced charge transport, and favorable morphology. This work demonstrates that the site of polymerization on SMAs strongly affects device performance, offering insights into the development of efficient polymer acceptors for all‐PSCs.

A new DPP‐based alternating D–A copolymer (PD2FCT‐29DPP) is developed for use as a hole‐transport layer. PD2FCT‐29DPP addresses the different requirements for an HTL, offering favorable energetics, near‐infrared absorption, and efficient charge transfer. Therefore, a PD2FCT‐29DPP‐based device achieves a remarkable FF of 70% and the highest PCE of 14.0% among PbS CQD‐SCs.

Abstract

The need for optoelectronic and chemical compatibility between the layers in colloidal quantum dot (CQD) photovoltaic devices remains a bottleneck in further increasing performance. Conjugated polymers are promising candidates as new hole‐transport layer (HTL) materials in CQD solar cells (CQD‐SCs) owing to the highly tunable optoelectronic properties and compatible chemistries. A diketopyrrolopyrrole‐based polymer with benzothiadiazole derivatives (PD2FCT‐29DPP) as an HTL in these devices is reported. The energy level, molecular orientation, and hole mobility of this HTL are manipulated through molecular engineering. By levering the polymer's optical absorption spectrum complementary to that of the CQD active layer, EQE across the visible and near‐infrared regions is maximized. As a result, a PD2FCT‐29DPP‐based device exhibits a fill factor of 70% and approximately 35% efficiency enhancement compared to a PTB7‐based device.

Microfabricated ion‐selective transistors with fast response and super‐Nernstian sensitivity are demonstrated. The remarkable performance arises from the use of a thin polyelectrolyte film as an internal ion reservoir between the ion‐selective membrane and the organic electrochemical transistor. The sensor architecture is generic and applicable to sensing of various ions, opening new frontiers for wearable and implantable ion sensors.

Abstract

Transistor‐based ion sensors have evolved significantly, but the best‐performing ones rely on a liquid electrolyte as an internal ion reservoir between the ion‐selective membrane and the channel. This liquid reservoir makes sensor miniaturization difficult and leads to devices that are bulky and have limited mechanical flexibility, which is holding back the development of high‐performance wearable/implantable ion sensors. This work demonstrates microfabricated ion‐selective organic electrochemical transistors (OECTs) with a transconductance of 4 mS, in which a thin polyelectrolyte film with mobile sodium ions replaces the liquid reservoir. These devices are capable of selective detection of various ions with a fast response time (≈1 s), a super‐Nernstian sensitivity (85 mV dec⁻¹), and a high current sensitivity (224 µA dec⁻¹), comparing favorably to other ion sensors based on traditional and emerging materials. Furthermore, the ion‐selective OECTs are stable with highly reproducible sensitivity even after 5 months. These characteristics pave the way for new applications in implantable and wearable electronics.

A thermally activated delayed fluorescence emitter, 2tDMG, is designed and synthesized based on the donor (D)/acceptor (A) spatially intramolecular noncovalent interaction. The D/A units are connected via a rigid linker, thereby confining them into a close‐packed coplanar configuration for small singlet–triplet splitting energy. 2tDMG achieves a high external quantum efficiency of 30.8% with a low efficiency roll‐off in evaporation‐processed organic light‐emitting diodes (OLEDs).

Abstract

In this work, two novel thermally activated delayed fluorescence (TADF) emitters, 2tDMG and 3tDMG, are synthesized for high‐efficiency organic light‐emitting diodes (OLEDs), The two emitters have a tilted face‐to‐face alignment of donor (D)/acceptor (A) units presenting intramolecular noncovalent interactions. The two TADF materials are deposited either by an evaporation‐process or by a solution‐process, both of them leading to high OLED performance. 2tDMG used as the emitter in evaporation‐processed OLEDs achieves a high external quantum efficiency (EQE) of 30.8% with a very flat efficiency roll‐off of 7% at 1000 cd m⁻². The solution‐processed OLEDs also display an interesting EQE of 16.2%. 3tDMG shows improved solubility and solution processability as compared to 2tDMG, and thus a high EQE of 20.2% in solution‐processed OLEDs is recorded. The corresponding evaporation‐processed OLEDs also reach a reasonably high EQE of 26.3%. Encouragingly, this work provides a novel strategy to address the imperious demands for OLEDs with high EQE and low roll‐off.

A straightforward polyTPD passivation is introduced to reduce the defect‐mediated recombination by elucidating the imperfections on the surface and grain boundaries of perovskite materials. Suppressed non‐radiative recombination and improved interfacial hole extraction result in perovskite solar cells with stabilized efficiency exceeding 21%. Moreover, ultra‐hydrophobic and thermally robust polyTPD passivated devices retain 94% of the initial efficiency after 800 h under operational conditions.

Abstract

The failure of perovskite solar cells (PSCs) to maintain their maximum efficiency over a prolonged time is due to the deterioration of the light harvesting material under environmental factors such as humidity, heat, and light. Systematically elucidating and eliminating such degradation pathways are critical to imminent commercial use of this technology. Here, a straightforward approach is introduced to reduce the level of defect‐states present at the perovskite and hole transporting layer interface by treating the various perovskite surfaces with poly(N,N′‐bis‐4‐butylphenyl‐N,N′‐bisphenyl)benzidine (polyTPD) molecules. This strategy significantly suppresses the defect‐mediated non‐radiative recombination in the ensuing devices and prevents the penetration of degrading agents into the inner layers by passivating the perovskite surface and grain boundaries. Suppressed non‐radiative recombination and improved interfacial hole extraction result in PSCs with stabilized efficiency exceeding 21% with negligible hysteresis (≈19.1% for control device). Moreover, ultra‐hydrophobic polyTPD passivant considerably alleviates moisture penetration, showing ≈91% retention of initial efficiencies after 300 h storage at high relative humidity of 80%. Similarly, passivated device retains 94% of its initial efficiency after 800 h under operational conditions (maximum power point tracking under continuous illumination at 60 °C). In addition to interfacial passivation function, hole‐selective role of dopant‐free polyTPD is also evaluated and discussed in this study.

High‐performance voltage‐dependent color‐tunable organic light‐emitting diodes (OLEDs) with a single Pt[O^{^}N^{^}C^{^}N] emitter are fabricated. The emission color can be tuned from warm white to natural white or from orange to yellowish green, depending upon the emitter used. High external quantum efficiency (23.23%), low efficiency roll‐off, long‐term stability (LT₉₀ = 19 105 h) and continuously variable color enable these color‐tunable OLEDs to find applications in smart wearable devices.

Abstract

Voltage‐dependent, color‐tunable organic light‐emitting diodes (OLEDs) are appealing tools that can be used for the visualization of electronic output signal of sensors. Nonetheless, the literature‐reported color‐tunable OLEDs that have a simple single‐cell device structure suffer from relatively low efficiency, pronounced efficiency roll‐off, color‐aging, and short operation lifetime, all of which limit their practical applications. Here, a novel co‐host‐in‐double‐emissive‐layer (CHIDEL) device, designed to enhance the performance of color‐tunable OLEDs with the use of a single tetradentate Pt[O^{^}N^{^}C^{^}N] emitter, is described. When Pt‐X‐2 is used as a single emitter in an optimized CHIDEL device, a white OLED with tunable Commission International de I'Eclairage (CIE) coordinates from (0.47, 0.44) at 3 V to (0.36, 0.48) at 11 V, a high color rendering index of 82, and high external quantum efficiency (EQE) of up to 20.75% can be achieved. By using Pt‐X‐4 as a single emitter, the voltage‐dependent color‐tunable CHIDEL device, with CIE coordinates shifted from (0.56, 0.43) at 3 V to (0.42, 0.55) at 11 V, demonstrates a high luminance of beyond 90 000 cd m⁻² and a high EQE of 23.23% at a luminance of 1300 cd m⁻². A long‐lifetime time to 90% of the initial luminance (LT₉₀) of almost 20 000 h is demonstrated for the color‐tunable OLED with Pt‐X‐4 emitting dopant.

Two ADA-type nonfullerene acceptors were designed and synthesized using a ladder-type fused-ring core that was free of sp3-hybridized bridging carbon atoms. The replacement of linear side chains with bulky branched side chains on the pyrrole units of the fused-ring core led to the nonfullerene acceptor (M3) with a dominantly face-on orientation. Thus, in combination with a donor polymer of PM6, M3 showed dramatically improved charge transport, consequently leading to a certified efficiency of 16.66% for the corresponding best performing device.

Novel asymmetric alkoxy and alkyl substitutions on the well‐known nonfullerene acceptor Y6 yield a molecule named Y6‐1O, and its photoelectric properties and photovoltaic performance are systematically compared with the two related symmetric molecules (Y6 and Y6‐2O), which suggests that this design strategy is promising and effective.

Abstract

In this paper, a strategy of asymmetric alkyl and alkoxy substitution is applied to state‐of‐the‐art Y‐series nonfullerene acceptors (NFAs), and it achieves great performance in organic solar cell (OSC) devices. Since alkoxy groups can have a significant influence on the material properties of NFAs, alkoxy substitution is applied to the Y6 molecule in a symmetric manner. The resulting molecule (named Y6‐2O), despite showing improved open‐circuit voltage (V _oc), yields extremely poor performance due to low solubility and excessive aggregation properties, a change that is due to the conformational locking effect of alkoxy groups. In contrast, asymmetric alkyl and alkoxy substitution on Y6, yields a molecule named Y6‐1O that can maintain the positive effect of V _oc improvement and obtain reasonably good solubility. The resulting molecule Y6‐1O enables highly efficient nonfullerene OSCs with 17.6% efficiency and the asymmetric side‐chain strategy has the potential to be applied to other NFA‐material systems to further improve their performance.

The photoinitiator bifunctional bis‐benzophenone is introduced into non‐fullerene solar cells as a multifunctional solid additive for the first time. The doping of this solid additive could not only modify the polymer order and firm morphology of active layer to improve device performance, but also to achieve better reproducibility, thickness insensitivity, and thermal stability for the non‐fullerene solar cells.

Abstract

Simultaneously improving efficiency and stability is critical for the commercial application of non‐fullerene acceptor polymer solar cells (NFA‐PSCs). Multifunctional solid additives have been considered as a potential route to tune the morphology of the active layer and optimize performance. In this work, photoinitiator bifunctional bis‐benzophenone (BP‐BP) is used as a solid additive, replacing solvent additives, in the PBDB‐T:ITIC NFA system. With the addition of BP‐BP, the intermolecular π–π stacking of PBDB‐T and morphology is improved, leading to more balanced carrier transport and more effective exciton dissociation. Devices fabricated with BP‐BP show a power conversion efficiency (PCE) of 11.89%, with enhanced short‐circuit current (J _sc), and fill factor (FF). Devices optimized with BP‐BP show excellent reproducibility, insensitivity to thickness, and an improved thermal stability under atmospheric conditions without encapsulation. This work provides a new strategy for the application of solid additives in NFA‐PSCs.

9.5% semitransparent solar cells with ultrahigh transmission in the visible range (50% AVT) are fabricated via inkjet printing. The effect of different photoactive layer ink solvents on the vertical stratification and performance is explored. The formulation of transport layer inks compatible with highly hydrophobic active layers and with scalable printing processes permits the use of a semitransparent electrode grid.

Abstract

New polymer donors and nonfullerene acceptors have elevated the performance and stability of solar cells to higher grounds. To achieve their full potential, they require their adaptation to scalable and cost‐effective solution manufacturing techniques for large area deposition. Likewise, formulating scalable solution‐based transport layer inks that are compatible with the photoactive layer is imperative. This manuscript reports the full integration of solution‐based transport layers and electrode alongside a PTB7‐Th:IEICO‐4F bulk heterojunction in inverted architecture through inkjet‐printing, resulting in power conversion efficiencies up to 12.4% opaque devices and 9.5% semitransparent devices with average visible transmittance values of 50.1%, including hole transport layer. The wetting envelope of the highly‐hydrophobic photoactive layer alongside the surface energy of candidate solutions and solvents allows the formulation of thick transport layer inks that are compatible with the drop‐on‐demand inkjet‐printing process and yield uniform and homogenous films. Moreover, the surface energy components of the donor and acceptor serves as a fingerprint to assess the vertical stratification of the photoactive layer with the inclusion of different solvents. This methodology addresses a scale‐up bottleneck of solution‐based transport layers for high‐efficiency organic cells, enabling its adaptation to high‐throughput techniques including slot‐die and roll‐to‐roll coating.