Yingzhi Jin

Accurate and correct measurements of photovoltaic figures of merit are crucial to aid the development of novel technologies such as perovskite solar cells. This perspective provides a critical assessment of the currently recommended practice of implementing photomasks during laboratory characterization of illuminated solar cells.

A naphthalene diimide (NDI)-based organic molecule (NDI-N) was prepared to be used as printable cathode interlayer (CIL) for organic solar cells (OSCs). NDI-N possesses combined advantages of high crystallinity and good film-forming properties, endowing the material with excellent electron-transport properties and good processability. NDI-N can be processed by printing methods; in this case an OSC device of 1 cm2 was fabricated by using blade-coated NDI-N and an efficiency of 13.2% was achieved, which represents the highest efficiency to date for large-area OSCs.

This research sheds light on the morphology of state-of-the-art nonfullerene organic solar cells (OSCs) from the perspective of thermodynamics and formation kinetics. We find that OSC morphology needs to be kinetically quenched for achieving optimal performance if the molecular interaction of constituent materials is too repulsive. The results provide useful guidelines for improving fabrication yield, reliability, and stability of a large class of high-performance OSCs.

A simple strategy to balance the voltage-current trade-off in tandem organic photovoltaics by employing mixed non-fullerene acceptors in rear sub-cells is reported. The tandem device with the best power conversion efficiency (PCE) of 13.3% was achieved in the lab. Importantly, the tandem devices were certified by the National Renewable Energy Laboratory (NREL) under the new protocols (asymptotic scans, which are much tougher than regular fast scans); a PCE of 11.52% was achieved and recognized on the most recent NREL chart.

To finely tune blend miscibility, a novel chemical tool of steric engineering is proposed. It renders a high PCE over 12% for the polymer with middle steric structure, due to a more balanced blend miscibility without sacrificing charge‐carrier transport. Therefore the steric effect‐induced miscibility (SEIM) as a novel chemical strategy exhibits very simple and promising potential in optimizing morphology.

Abstract

Morphology and miscibility control are still a great challenge in polymer solar cells. Despite physical tools being applied, chemical strategies are still limited and complex. To finely tune blend miscibility to obtain optimized morphology, chemical steric engineering is proposed to systemically investigate its effects on optical and electronic properties, especially on a balance between crystallinity and miscibility. By changing the alkylthiol side chain orientation different steric effects are realized in three different polymers. Surprisingly, the photovoltaic device of the polymerPTBB‐m with middle steric structure affords a better power conversion efficiency, over 12%, compared to those of the polymers PTBB‐o and PTBB‐p with large or small steric structures, which could be attributed to a more balanced blend miscibility without sacrificing charge‐carrier transport. Space charge‐limited current, atomic force microscopy, grazing incidence wide angle X‐ray scattering, and resonant soft X‐ray scattering measurements show that the steric engineering of alkylthiol side chains can have significant impacts on polymer aggregation properties, blend miscibility, and photovoltaic performances. More important, the control of miscibility via the simple chemical approach has preliminarily proved its great potential and will pave a new avenue for optimizing the blend morphology.

Design and application of volatilizable solid additives in non-fullerene organic solar cells

Design and application of volatilizable solid additives in non-fullerene organic solar cells, Published online: 07 November 2018; doi:10.1038/s41467-018-07017-z

High-boiling-point solvent additives are commonly used to optimize the device performance of organic solar cells but they make problems for device stability and reproducibility. Here Yu et al. design volatilizable solid additives that can improve the device performance without causing above issues.

Advanced Energy Materials, Volume 8, Issue 36, December 27, 2018.

Advanced Energy Materials, Volume 8, Issue 36, December 27, 2018.

Charge and triplet exciton dynamics in neat fullerene and hybrid solar cells with fullerene as the only light absorber are investigated by transient spectroscopy. The efficiency and mechanism of charge generation and triplet formation depend on the photoactive layer composition. Formation of a hybrid bulk heterojunction leads to ultrafast exciton dissociation, fast charge extraction, and power conversion efficiencies in excess of 5%.

Abstract

Organic solar cells that use only fullerenes as the photoactive material exhibit poor exciton‐to‐charge conversion efficiencies, resulting in low internal quantum efficiencies (IQE). However, the IQE can be greatly improved, when copper(I) thiocyanate (CuSCN) is used as a carrier‐selective interlayer between the phenyl‐C70‐butyric acid methyl ester (PC₇₀BM) layer and the anode. Efficiencies of ≈5.4% have recently been reported for optimized CuSCN:PC₇₀BM (1:3)‐mesostructured heterojunctions, yet the reasons causing the efficiency boost remain unclear. Here, transient absorption (TA) spectroscopy is used to demonstrate that CuSCN does not only act as a carrier‐selective electrode layer, but also facilitates fullerene exciton dissociation and hole transfer at the interface with PC₇₀BM. While intrinsic charge generation in neat PC₇₀BM films proceeds with low yield, hybrid films exhibit much improved exciton dissociation due to the presence of abundant interfaces. Triplet generation with a rate proportional to the product of singlet and charge concentrations is observed in neat PC₇₀BM films, implying a charge–singlet spin exchange mechanism, while in hybrid films, this mechanism is absent and triplet formation is a consequence of nongeminate recombination of free charges. At low carrier concentrations, the fraction of charges outweighs the population of triplets, leading to respectable device efficiencies under one sun illumination.

The absence of a charge transfer (CT) state is found in the (6,5) single‐walled carbon nanotube:PC₇₀BM system and a detailed analysis of the open‐circuit voltage (V _OC) is reported. The analysis reveals that the lack of the CT state enables very small radiative as well as nonradiative V _OC losses for an organic cell, despite the ultranarrow bandgap of this system.

Abstract

Current state‐of‐the‐art organic solar cells (OSCs) still suffer from high losses of open‐circuit voltage (V _OC). Conventional polymer:fullerene solar cells usually exhibit bandgap to V _OC losses greater than 0.8 V. Here a detailed investigation of V _OC is presented for solution‐processed OSCs based on (6,5) single‐walled carbon nanotube (SWCNT): [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester active layers. Considering the very small optical bandgap of only 1.22 eV of (6,5) SWCNTs, a high V _OC of 0.59 V leading to a low E _gap/q − V _OC = 0.63 V loss is observed. The low voltage losses are partly due to the lack of a measurable charge transfer state and partly due to the narrow absorption edge of SWCNTs. Consequently, V _OC losses attributed to a broadening of the band edge are very small, resulting in V _OC,SQ − V _OC,rad = 0.12 V. Interestingly, this loss is mainly caused by minor amounts of SWCNTs with smaller bandgaps as well as (6,5) SWCNT trions, all of which are experimentally well resolved employing Fourier transform photocurrent spectroscopy. In addition, the low losses due to band edge broadening, a very low voltage loss are also found due to nonradiative recombination, ΔV _OC,nonrad = 0.26 V, which is exceptional for fullerene‐based OSCs.

Four new polymers containing the novel asymmetrical backbone, thienobenzodithiophene, are synthesized and applied in high‐performance nonfullerene solar cells. The asymmetrical backbone can dramatically effect the polymer geometric configuration and modulate the polymer aggregation and crystallinity. This work reveals that the versatile asymmetric backbone is an excellent moiety to construct light‐harvesting copolymers and to modulate the microstructure for highly efficient PSCs.

Abstract

In this work, a new asymmetrical backbone thienobenzodithiophene (TBD) containing four aromatic rings is designed, and then four polymers PTBD‐BZ, PTBD‐BDD, PTBD‐FBT, and PTBD‐Tz are synthesized. The planar and high degree of π‐conjugation configuration can guarantee effective charge carrier transport and the distinct flanked dihedral angles between the TBD core and conjugated side chain can subtly regulate the molecular aggregation and crystallinity. The four polymer/3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone)‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]‐dithiophene (ITIC) blending films exhibit predominantly face‐on orientation. The photovoltaic devices based on wide bandgap polymers PTBD‐BZ and PTBD‐BDD achieve power conversion efficiencies (PCEs) as high as 12.02% and 11.39% without any post‐treatment. For the medium bandgap polymers PTBD‐FBT and PTBD‐Tz, the devices also show good PCEs of 10.18% and 11.02% with high V _OC of 0.94 and 1.02 V, respectively, which indicates simultaneously achieving a V _OC > 1 V and a high J _SC is feasible to further improve the PSCs' performance by modifying this new backbone. This work reveals that the versatile asymmetric backbone is an excellent moiety to construct light‐harvesting copolymers and to modulate the microstructure for highly efficient PSCs.

A high‐performance (12.9%) non‐fullerene organic solar cell processed using a sequential bilayer deposition method from non‐halogenated solvents is reported. Using this method, the organic solar cell can be scaled up to a larger area (1 cm²) while maintaining a high performance of 11.4% by doctor‐blade coating. This method offers a truly compatible processing technique for printing large area organic solar cell modules.

Abstract

While the performance of laboratory‐scale organic solar cells (OSCs) continues to grow over 13%, the development of high‐efficiency large area OSCs still lags. One big challenge is that the formation of bulk heterojunction morphology is an extremely complicated process and the formed morphology is also a highly delicate balance involving many parameters such as domain size, purity, miscibility, etc. The morphology control becomes much more challenging when the device area is scaled up. In this work, a highly efficient (12.9%) nonfullerene organic solar cell processed using a sequential bilayer deposition method from nonhalogenated solvents, is reported. Using this bilayer processing method, the organic solar cells can be scaled up to a larger area (1 cm²) while maintaining a high performance of 11.4% using doctor‐blade‐coating technique. Moreover, as the acceptor is hidden behind the polymer donor, the possibility of degradation by sunlight is lessened. Thus, improved photostability is observed in the bilayer structure device when compared with the bulk heterojunction device. This method offers a truly compatible processing technique for printing large‐area OSC modules.

Linear correlation of fill factor and relative standard deviation of fullerene distribution reveals that a ternary blend morphology with a uniform and pure mixed amorphous domain is required to achieve efficient ternary solar cells. This is achieved by the right kinetic path, controlled by the material and process compatibility.

Abstract

Although ternary solar cells (TSCs) offer a cost‐effective prospect to expand the absorption bandwidth of organic solar cells, only few TSCs have succeeded in surpassing the performance of binary solar cells (BSCs) primarily due to the complicated morphology of the ternary blends. Here, the key factors that create and limit the morphology and performance of the TSCs are elucidated. The origin of morphology formation is explored and the role of kinetic factors is investigated. The results reveal that the morphology of TSC blends considered in this study are characterized with either a single length‐scale or two length‐scale features depending on the composition of the photoactive polymers in the blend. This asymmetric morphology development reveals that TSC blend morphology critically depends on material compatibility and polymer solubility. Most interestingly, the fill factor (FF) of TSCs is found to linearly correlate with the relative standard deviation of the fullerene distribution at small lengths. This is the first time that such a correlation has been shown for ternary systems. The criteria that uniform sized and highly pure amorphous domains are accomplished through the correct kinetic path to obtain a high FF for TSCs are specifically elucidated. The findings provide a critical insight for the precise design and processing of TSCs.

Spectral engineering and ternary blend approaches were employed to demonstrate an efficient semitransparent polymer solar cell tailored for greenhouse application. The semitransparent device transmits mainly blue and red lights for photosynthesis, and shows a high efficiency of 7.75% with a crop growth factor of 24.8%. Optimal sunlight harvesting in photovoltaics and photosynthesis will be beneficial for future greenhouse application.

Abstract

In this study, a wavelength selective semitransparent polymer solar cell (ST‐PSC) with a proper transmission spectrum for plant growth is proposed for greenhouse applications. A ternary strategy combining a wide bandgap polymer donor with a near‐infrared absorbing nonfullerene acceptor and a high electron mobility fullerene acceptor is introduced to achieve PSCs with power conversion efficiency (PCE) over 10%. The addition of PC₇₁BM into J52:IEICO‐4F binary blend contributes to the suppressed trap‐assisted recombination, enhanced charge extraction, and improved open‐circuit voltage simultaneously. ST‐PSC based on the J52:IEICO‐4F:PC₇₁BM ternary blend shows an optimized performance with PCE of 7.75% and a defined crop growth factor of 24.8%. Such high‐performance ST‐PSC is achieved by carefully engineering the absorption spectrum of the light harvesting materials. As a result, the transmission spectra of the semitransparent devices are well‐matched with the absorption spectra of the photoreceptors, such as chlorophylls, in green plants, which provides adequate lighting conditions for photosynthesis and plant growth, and therefore making it a competitive candidate for photovoltaic greenhouse applications.

F4‐TCNQ is applied to manipulate the morphological, electrical, and photovoltaic properties of nonfullerene solar cells. Adding a trace amount of F4‐TCNQ yields a higher current density and fill factor, in comparison to the reference device. The combined techniques evidence that the addition of F4‐TCNQ increases charge lifetime, charge mobility, and mean‐square composition variation.

Abstract

Fluorinated molecule 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4‐TCNQ) and its derivatives have been used in polymer:fullerene solar cells primarily as a dopant to optimize the electrical properties and device performance. However, the underlying mechanism and generality of how F4‐TCNQ affects device operation and possibly the morphology is poorly understood, particularly for emerging nonfullerene organic solar cells. In this work, the influence of F4‐TCNQ on the blend film morphology and photovoltaic performance of nonfullerene solar cells processed by a single halogen‐free solvent is systematically investigated using a set of morphological and electrical characterizations. In solar cells with a high‐performance polymer:small molecule blend FTAZ:IT‐M, F4‐TCNQ has a negligibly small effect on the molecular packing and surface characteristics, while it clearly affects the electronic properties and mean‐square composition variation of the bulk. In comparison to the control devices with an average power conversion efficiency (PCE) of 11.8%, inclusion of a trace amount of F4‐TCNQ in the active layer has improved device fill factor and current density, which has resulted into a PCE of 12.4%. Further increase in F4‐TCNQ content degrades device performance. This investigation aims at delineating the precise role of F4‐TCNQ in nonfullerene bulk heterojunction films, and thereby establishing a facile approach to fabricate highly optimized nonfullerene solar cells.

Strong coupling is an intriguing phenomenon where a physical system is generated through the interaction of two or more components. Transient absorption spectroscopy, a thoroughly validated technique for studying strong coupling, is based on a pump‐probe solution, and can follow the energy relaxation of strongly coupled systems over time. In article number 1801761, Hai Wang, Remo Proietti Zaccaria, and co‐workers present some of the most important results achieved in this field to date.

Multichannel strategies involving modulation of the counterions, end‐capped substituents, and dimerization are established to regulate the concentrations of azaphenalene diradicals for the first time. The generated anion‐radicals substantially decrease the work functions of the cathode. The all‐solution‐processed bulk heterojunction organic solar cells fabricated with azaphenalene salts based cathode interfacial layers achieve a high power conversion efficiency over 10%.

Abstract

Self‐doped cathode interfacial layers (CILs) are crucial to enable Ohmic‐like contact between the electrode and organic functional layers and thus profoundly promote the performances of organic optoelectronic devices. Herein, multifarious azaphenalene‐embedded organic salts with variable counterions, substituent groups, and repeating units are prepared, and their impacts on producing homologous diradicals are established. Electron paramagnetic resonance and X‐ray photoelectron spectroscopy studies reveal the existence of free radicals of these azaphenalene salts in the solid state. Density functional theory simulations indicate that the thermal energy of counterion‐induced proton transfer is crucial to produce diradicaloids, which can be manipulated in tailoring the azaphenalene backbones. Noticeably, the formed diradicaloids that are delocalized over the π‐conjugated systems will be beneficial to enhance the carrier density of the matrix and remarkably decrease the work functions of the Al electrode. The all‐solution‐processed bulk heterojunction organic solar cells are fabricated by employing them as CILs, which results in high power conversion efficiency of 10.24% in contrast to the 7.34% of the reference device without CILs.

Fine-tuning of the chemical structure of photoactive materials for highly efficient organic photovoltaics

Fine-tuning of the chemical structure of photoactive materials for highly efficient organic photovoltaics, Published online: 22 October 2018; doi:10.1038/s41560-018-0263-4

Materials design rules play a key role in enabling high performance in organic photovoltaics. Here the authors achieve 12.25% efficiency on 1 cm2 non-fullerene solar cells by tuning the side chains’ branching point and the fluorine substitutions in donor and acceptor materials.

Near‐infrared nonfullerene acceptors (NIR NFAs, T1–T4) with fluorinated regioisomeric A–Aπ–D–Aπ–A backbones are developed for high‐performance polymer solar cells (PSCs), in which proximal NFAs with varied F‐atoms (T1–T3) largely outperform distal NFA (T4). Particularly, single‐junction PSCs with a PTB7‐Th:T2 blend can achieve 10.87% power conversion efficiency (PCE), and tandem PSCs through integrating with an ITIC:PBDB‐T blend reach a PCE of 14.64%.

Abstract

Solar photon‐to‐electron conversion with polymer solar cells (PSCs) has experienced rapid development in the recent few years. Even so, the exploration of molecules and devices in efficiently converting near‐infrared (NIR) photons into electrons remains critical, yet challenging. Herein presented is a family of near‐infrared nonfullerene acceptors (NIR NFAs, T1–T4) with fluorinated regioisomeric A–Aπ–D–Aπ–A backbones for constructing efficient single‐junction and tandem PSCs with photon response up to 1000 nm. It is found that the tuning of the regioisomeric bridge (Aπ) and fluoro (F)‐substituents on a molecular skeleton strongly influences the backbone conformation and conjugation, leading to the optimized optoelectronic and stable stacking of resultant NFAs, which eventually impacts the performance of derived PSCs. In PSCs, the proximal NFAs with varied F‐atoms (T1–T3) mostly outperform than that of distal NFA (T4). Notably, single‐junction PSC with PTB7‐Th:T2 blend can reach 10.87% power conversion efficiency (PCE), after implementing a solvent additive to improve blend morphology. Moreover, efficient tandem PSCs are fabricated through integrating such NIR cells with mediate bandgap nonfullerene‐based subcells, to achieve a PCE of 14.64%. The results reveal the structural design of organic semiconductor and device with improved photovoltaic performance.

The utilization of poly(vinylpyrrolidone) (PVP) as a cathode interlayer is demonstrated in inverted and conventional devices via both the self‐organization method and the step‐by‐step preparation method. The driving forces for PVP migration are the high surface energy of the PVP and the strong intermolecular interaction between the PVP and the bottom cathode. In addition, the PVP‐modified devices have excellent stability in air and show insensitivity to PVP molecular weight.

Abstract

Herein, poly(vinylpyrrolidone) (PVP) is used as the cathode interlayer (CIL) through the self‐organization method in inverted organic solar cells (OSCs). By coating a solution of PVP and active layer materials onto a glass/indium tin oxide (ITO) substrate, the PVP can segregate to the near ITO side due to its high surface energy and strong intermolecular interaction with the ITO electrode. The power conversion efficiency (PCE) of the obtained OSC device reaches 13.3%, much higher than that of the control device with a PCE of only 10.1%. The improvement results from the increased exciton dissociation efficiency and the depressed trap‐assisted recombination, which can be attributed to the reduced work function of the cathode by the self‐organized PVP. Additionally, the molecular weight of the PVP has almost no influence on the device performance, and the PVP‐modified device presents superior stability. This method can also be applied in other highly efficient fullerene‐free OSCs, and with a fine selection of the active layer, a high PCE of 14.0% is obtained. Overall, this work demonstrates the great potential of the PVP‐based CIL in inverted OSCs fabricated via the self‐organization method.

Utilizing multiple donor–acceptor pairs for organic solar cells (OSCs) is a very effective strategy for overcoming the limitations of conventional OSCs based on a single donor–acceptor pair. Recent cases of OSCs with multiple donor–acceptor pairs are not only summarized but their perspectives are also presented.

Abstract

Compared with conventional organic solar cells (OSCs) based on single donor–acceptor pairs, terpolymer‐ and ternary‐based OSCs featuring multiple donor–acceptor pairs are promising strategies for enhancing the performance while maintaining an easy and simple synthetic process. Using multiple donor–acceptor pairs in the active layer, the key photovoltaic parameters (i.e., short‐circuit current density, open‐circuit voltage, and fill factor) governing the OSC characteristics can be simultaneously or individually improved by positive changes in light‐harvesting ability, molecular energy levels, and blend morphology. Here, these three major contributions are discussed with the aim of offering in‐depth insights in combined terpolymers and ternary systems. Recent exemplary cases of OSCs with multiple donor–acceptor pairs are summarized and more advanced research and perspectives for further developments in this field are highlighted.

The rapid development in large‐area organic solar cells (OSCs) is reviewed. Materials requirements, modular designs, and printing methods for large‐area OSCs are discussed. By combining thick‐film material systems with efficient modular designs, and then by employing the right printing methods, the fabrication of large‐area OSCs will be successfully realized in the near future.

Abstract

The printing of large‐area organic solar cells (OSCs) has become a frontier for organic electronics and is also regarded as a critical step in their industrial applications. With the rapid progress in the field of OSCs, the highest power conversion efficiency (PCE) for small‐area devices is approaching 15%, whereas the PCE for large‐area devices has also surpassed 10% in a single cell with an area of ≈1 cm². Here, the progress of this fast developing area is reviewed, mainly focusing on: 1) material requirements (materials that are able to form efficient thick active layer films for large‐area printing); 2) modular designs (effective designs that can suppress electrical, geometric, optical, and additional losses, leading to a reduction in the PCE of the devices, as a consequence of substrate area expansion); and 3) printing methods (various scalable fabrication techniques that are employed for large‐area fabrication, including knife coating, slot‐die coating, screen printing, inkjet printing, gravure printing, flexographic printing, pad printing, and brush coating). By combining thick‐film material systems with efficient modular designs exhibiting low‐efficiency losses and employing the right printing methods, the fabrication of large‐area OSCs will be successfully realized in the near future.

A desirable water–ethanol process is developed for ecofriendly and nonhazardous fabrication of polymer electronic devices. The addition of a typical antisolvent, water, to ethanol remarkably improves the solubility of nonionic oligoethylene glycol side chain‐based electroactive materials, which enables the fabrication of efficient and air‐stable organic field‐effect transistors and polymer solar cells.

Abstract

The authors report the development of a desirable aqueous process for ecofriendly fabrication of efficient and stable organic field‐effect transistors (eco‐OFETs) and polymer solar cells (eco‐PSCs). Intriguingly, the addition of a typical antisolvent, water, to ethanol is found to remarkably enhance the solubility of oligoethylene glycol (OEG) side chain‐based electroactive materials (e.g., the highly crystalline conjugated polymer PPDT2FBT‐A and the fullerene monoadduct PC₆₁BO₁₂). A water–ethanol cosolvent with a 1:1 molar ratio provides an increased solubility of PPDT2FBT‐A from 2.3 to 42.9 mg mL⁻¹ and that of PC₆₁BO₁₂ from 0.3 to 40.5 mg mL⁻¹. Owing to the improved processability, efficient eco‐OFETs with a hole mobility of 2.0 × 10⁻² cm² V⁻¹ s⁻¹ and eco‐PSCs with a power conversion efficiency of 2.05% are successfully fabricated. In addition, the eco‐PSCs fabricated with water–ethanol processing are highly stable under ambient conditions, showing the great potential of this new process for industrial scale application. To better understand the underlying role of water addition, the influence of water addition on the thin‐film morphologies and the performance of the eco‐OFETs and eco‐PSCs are studied. Additionally, it is demonstrated that the application of the aqueous process can be extended to a variety of other OEG‐based material systems.

Large‐area, semitransparent, and flexible all‐polymer photodetectors are realized by incorporating a pair of donor and acceptor polymers and by using a lamination method. Both sides of these all‐polymer photodetectors respond visible light signals with nearly identical D* over 1.0 × 10¹¹ Jones.

Abstract

Photodetectors, converting optical signals from specific wavelengths to electrical signals, have many applications on photoimaging, optical communication, and environmental monitoring. Solution‐processed organic photodetectors (OPDs) based on organic materials emerge promise especially for wearable electronics and smart buildings. In this work, new all‐polymer photodetectors (all‐PPDs) are developed based on bulk‐heterojunction active layers which incorporate a donor polymer and an acceptor polymer. The inverted all‐PPDs exhibit outstanding external quantum efficiency over 70%, low dark current density (J _d) of 1.1 × 10⁻⁸ A cm⁻², and high detectivity (D*) over 3.0 × 10¹² Jones with planar response over the entire visible range. It is one of the best‐performing all‐PPDs reported so far and is also comparable with many organic and inorganic photodetectors. By using lamination technique, large‐area, semitransparent, flexible, and “fully” polymeric photodetectors are successfully fabricated for the first time, with D* over 10¹¹ Jones for double‐side light detection. The results highlight the great potential for producing high‐performance all‐PPDs by taking advantages of various device architecture and solution‐processing techniques.

A balanced crystallinity of donor and acceptor is finely controlled by combining blade‐coating and ternary strategies in a PBDB‐T:PTB7‐Th:FOIC‐based organic solar cell, resulting in well‐matched hole and electron mobilities with a power conversion efficiency of 12.02%.

Abstract

As a prototype tool for slot‐die coating, blade‐coating exhibits excellent compatibility with large‐area roll‐to‐roll coating. A ternary organic solar cell based on PBDB‐T:PTB7‐Th:FOIC blends is fabricated by blade‐coating and exhibits a power conversion efficiency of 12.02%, which is one of the highest values for the printed organic solar cells in ambient environment. It is demonstrated that blade‐coating can enhance crystallization of these three materials, but the degree of induction is different (FOIC > PBDB‐T > PTB7‐Th). Thus, the blade‐coated PBDB‐T:FOIC device presents much higher electron mobility than hole mobility due to the very high crystallinity of FOIC. Upon the addition of PTB7‐Th into the blade‐coated PBDB‐T:FOIC blends, the crystallinity of FOIC decreases together with the corresponding electron mobility, due to the better miscibility between PTB7‐Th and FOIC. The ternary strategy not only maintains the well‐matched crystallinity and mobilities, but also increases the photocurrent with complementary light absorption as well as the Förster resonant energy transfer. Furthermore, small domains with homogeneously distributed nanofibers are observed in favor of the exciton dissociation and charge transport. This combination of blade‐coating and ternary strategies exhibits excellent synergistic effect in optimizing morphology, showing great potential in the large‐area fabrication of highly efficient organic solar cells.