Yingzhi Jin

A coherent interface of PMA₂PbI₄ and FAPbI₃ induces epitaxial growth of α‐FAPbI₃. Facilitated formation of α‐FAPbI₃ at low temperature results in minimal structural disorder and enhanced charge‐carrier transport properties. A perovskite solar cell based on PMA₂PbI₄ and Cs_0.02FA_0.98PbI₃ exhibits an efficiency of 21.25% and stabilized efficiency of 19.95%.

Abstract

Low dimensional (LD) perovskite materials generally exhibit superior chemical stability against ambient moisture and thermal stress than that of 3D perovskites. Recently, LD perovskite has been used as a passivation layer on the surface of 3D perovskite grains. Although various LD perovskites have been developed focusing on their hydrophobicity, the impact of crystal structure of LD perovskite on the photovoltaic performance of perovskite solar cell (PSC) is still uncertain. In this work, the effects of the structural characteristics of LD perovskites on the crystal formation of formamidinium lead triiodide (α‐FAPbI₃) and on the optoelectrical properties of PSCs are elucidated. The phase‐transformation kinetics of FAPbI₃ mixed with LD perovskites is studied using the Johnson–Mehl–Avrami–Kolmogorov model. It is found that the arrangement of PbI₆ octahedra in the LD perovskite changes the rate of α‐FAPbI₃ formation. Facilitated nucleation of α‐FAPbI₃ at the LD/FAPbI₃ interface results in minimal structural disorder and prolonged charge‐carrier lifetimes. As a result, the PSC with the optimized LD perovskite structure exhibits a power conversion efficiency of 21.25% from a reverse current–voltage scan, and stabilized efficiency of 19.95% with excellent ambient stability without being encapsulated.

Charge transfer state parameterization based upon external quantum efficiency and electroluminescent is influenced by cavity effects yielding arbitrary results. This is shown to be due to the thickness dependent cavity in(out)put coupling. A practical approach is presented to overcome this issue. The effect is demonstrated in several organic solar cells including non‐fullerene‐based devices.

Abstract

Free carrier photogeneration in bulk‐heterojunction solar cells composed of blends of acceptor and donor organic semiconductors proceeds via intermolecular charge transfer (CT) states. Non‐adiabatic Marcus theory has proven valid to explain the absorption and emission of these sub‐gap states which have extremely weak emission probabilities and absorption cross sections making them difficult to probe directly using optical spectroscopy. Therefore, the CT state parameters involved in the Marcus model are often extracted from fittings on the photovoltaic external quantum efficiency (EQE _PV) and electroluminescence. These two spectra are (ideally) interrelated via the so‐called reciprocity principle. In this paper, the limitations of such an approach are demonstrated, in particular the impact of simple low finesse cavity interference effects acting as an uneven spectral filter for emission and absorption. This can produce almost spurious CT state parameterization with, for example, relative errors as large as 90% in absorption coefficients obtained from EQE _PV. It is shown how these limitations can be partially lifted using an iterative transfer matrix approach applied to the EQE _PV.

Stable and pure α‐FAPbI₃ phase is successfully obtained by a printed method in the ambient atmosphere. The scalable and fully printed perovskite solar cell with a carbon top electrode provides a stable PCE of 16.4%, which is the highest performance of full printed FAPbI₃ PSCs reported to date.

Abstract

Manufacturing commercially viable perovskite solar cells still requires appropriate low‐temperature and scalable deposition processes to be developed. While α‐phase FAPbI₃ has higher thermal stability and broader absorption than MAPbI₃, there still is no report of a pure α‐phase FAPbI₃ perovskite film obtained by a scalable printing method. Moreover, spontaneous conversion of the α‐phase to non‐perovskite δ‐phase under ambient conditions poses a serious challenge for practical applications. Herein, a scalable and fully solution based printing method for the fabrication of pure α‐phase FAPbI₃ perovskite solar cells is reported. Through adding N‐methyl pyrrolidone and methylammonium chloride to the dimethylformamide based precursor solution to control the crystallization, and vacuum or air‐flow assisted film drying, pure α‐FAPbI₃ phase is obtained by doctor blading. The resulting α‐FAPbI₃ film is highly stable, with no δ‐FAPbI₃ phase being formed even after keeping it in an ambient atmosphere over a period of 200 days without encapsulation. In addition, a fully solution processed PSC with a PCE of 16.1% is processed by the vacuum assisted method, and 17.8% by the air‐flow assisted method. Replacing silver with a printed carbon electrode provides a stable PCE up to 15% for the vacuum assisted and 16.4% for the air‐flow assisted method, which is the highest performance of FAPbI₃ solar cells to date. Compared with MAPbI₃, the fully printed FAPbI₃ perovskite devices exhibit a remarkable thermal stability in humid atmospheres which makes them a promising candidate for scalable production and commercialization.

This essay provides key innovations in design and fabrication of conjugated polymer nanomaterials such as polymer dots, conjugated polyelectrolytes, 2D polymer nanosheets, and polymer nanocomposites for photocatalytic H₂/O₂ evolution and overall water splitting. In addition, the challenges and opportunities for the future exploration of conjugated polymer nanophotocatalysts are discussed.

Abstract

Exploration of robust and inexpensive photocatalysts for direct water splitting is highly desirable for solar energy utilization but remains a great challenge. Although some inorganic semiconductors have shown very promising activities, many suffer from low quantum efficiency and insufficient sunlight absorption or present environmental hazards. In recent years, conjugated polymer nanomaterials have rapidly become one of the most appealing candidates in photocatalysis, owing to their facile molecular functionalization, tunable optoelectronic properties, and good chemical stability. This essay highlights the recent advancement of conjugated polymer nanomaterials for solar water splitting. The research opportunities related to water photolysis together with the perspective and challenges in the field are discussed to inspire further exciting research in water splitting.

The reported hierarchically designed light‐trapping system effectively confines light inside bifacially operating semitransparent photovoltaics. The trapping system consists of two asymmetric‐reflection surfaces, which exclusively permit the one‐way transmission of the incident light. All‐day operating semitransparent photovoltaics developed herein simultaneously exhibit the properties of a nearly black absorber and high‐performance current generation under solar and artificial light illumination.

Abstract

Highly efficient light‐trapping polymer films are designed to enhance the photocurrent of semitransparent organic photovoltaics (ST‐OPVs) in indoor and outdoor conditions. An asymmetric‐reflection film fabricated through the novel combination of randomly arranged nanostructures with periodically assembled microstructures exhibits selectivity for the direction of incident light. The film effectively traps light within the device by selectively reflecting light that escapes from the inside out. Moreover, this light‐trapping effect is maximized by attaching the films to both sides of the bifacial ST‐OPVs operating under solar and indoor sources, simultaneously. Accordingly, the light‐trapping polymer film platform presents short‐circuit current density (  J _SC) enhancement of ST‐OPVs by 13.49% and 46.19% under air mass 1.5G and light‐emitting diodes (1000 lux) illumination, respectively, and provides new opportunities for ST‐OPVs in a variety of practical applications.

Poly(3,4‐ethylenedioxythiophene) coated TiON//VN asymmetric microsupercapacitors (AMSCs) with interwoven nanowire network microelectrodes are fabricated by a novel facile method. Benefitting from the high electron/ion conductivity of the nanowire network, the AMSC achieves a high energy density of 32.4 μWh cm⁻² (at 1 mA cm⁻²) and a power density of 45 mW cm⁻² (at 50 mA cm⁻²).

Abstract

On‐chip microsupercapacitors (MSC) with facile fabrication procedures, high integration design, and superior performance are desired as an energy storage device for microelectronics. Hence, a novel procedure is proposed to fabricate an asymmetric microsupercapacitor (AMSC), employing interwoven nanowire (NW) network electrodes of poly(3,4‐ethylenedioxythiophene) coated titanium oxynitride (P‐TiON) and vanadium nitride (VN) NW as a cathode and an anode, respectively. The interwoven NWs with a high mass loading offer a sufficient electrochemical reaction area and rapid electron/ion transport pathway, delivering superior energy and power densities. With the LiCl/polyvinyl alcohol electrolyte, the assembled P‐TiON//VN AMSC can achieve a wide voltage window from 0 to 1.8 V with an excellent areal capacitance of 72 mF cm⁻², a high areal energy density of 32.4 μWh cm⁻² (at 0.9 mW cm⁻²), an outstanding power density of 45 mW cm⁻² (at 21.9 μWh cm⁻²), and a good cycling performance. Furthermore, the substrate‐free electrodes exhibit outstanding integrability, and the system on one printed circuit board including two AMSCs in series and a LED demonstrates excellent practicability.

Organic photovoltaics (OPVs) demostrate certified cell efficiencies of over 17% and are expected to contribute to versatile applications powered by solar energy. By taking into consideration different critical and “soft” key performance indicators, this work demonstrates material strategies to accelerate the development of OPV technology toward a GW era.

Abstract

With the rise of the solar power century, photovoltaic applications and installations will go beyond the traditional green field power plants and enter any aspect of daily life. Organic photovoltaics (OPVs) demonstrate certified cell efficiencies of over 17% and are expected to contribute to versatile applications powered by solar energy, for instance, applications rely on flexibility, transparency, color management, or integrability. In this work, the progress of OPV technology is briefly reviewed and the material strategies to accelerate OPV technology toward a GW era are analyzed. In addition to the exciting efficiency values achieved for small area devices, there are many important criteria deciding the success of OPV technology. By taking into consideration the synthetic complexity of OPV materials and the operational stability of OPV devices, the industrial figure of merit (i‐FoM) is proposed as a fast and reliable method to verify the true potential of a novel material. Furthermore, “soft” key performance indicators are introduced, such as toxicity, flexibility, transparency, processing, which require different development strategies to reflect the potential of OPV technology for specific applications.

Three dithienylphenylene‐bridged diketopyrrolopyrrole dimers, linked in ortho (o‐DPP), meta (m‐DPP), and para (p‐DPP) positions, are characterized in the context of intramolecular singlet fission (i‐SF). In the cases of o‐DPP and m‐DPP, SF is mediated by a charge transfer state, while population of a symmetry‐breaking charge‐separated state dominates p‐DPP and, in turn, hampers SF.

Abstract

Three diketopyrrolopyrrole (DPP) dimers, linked via different dithienylphenylene spacers, ortho‐DPP (o‐DPP), meta‐DPP (m‐DPP), and para‐DPP (p‐DPP), are synthesized, characterized, and probed in light of intramolecular singlet fission (i‐SF). Importantly, the corresponding DPP reference (DPP‐Ref) singlet and triplet excited state energies of 2.22 and 1.04 eV, respectively, suggest that i‐SF is thermodynamically feasible. The investigations focus on the impact of the relative positioning of the DPPs, and give compelling evidence that solvent polarity and/or spatial overlap govern i‐SF dynamics and efficiencies. Polar solvents make the involvement of an intermediate charge transfer (CT) state possible, followed by the population of ¹(T₁T₁) and subsequently (T₁ + T₁), while spatial overlap drives the mutual interactions between the DPPs. In o‐DPP, the correct balance between polar solvents and spatial overlap leads to the highest triplet quantum yield (TQY) of 40%. Notable is the superimposition of CT and triplet excited states, preventing an accurate TQY determination. For m‐DPP, poorer spatial overlap correlates with weaker CT character and manifests in a TQY of 11%. Strong CT character acts as a trap and prevents i‐SF, as found with p‐DPP. The DPP separation is decisive, enabling a symmetry‐breaking charge‐separated state rather than CT formation, shutting down the formation ¹(T₁T₁).

Thermal annealing of 2D/3D perovskite heterostructures leads to beneficial diffusion passivation; however, it also causes lattice expansion of the 2D perovskite. Here a novel preparation strategy, simultaneously inhibiting lattice expansion, compensating the large tensile stress of 2D perovskite, and inducing diffusion passivation, is introduced. As a result, a certified efficiency of 20.22% is obtained.

Abstract

Lattice matching and passivation are generally seen as the main beneficial effects in 2D/3D perovskite heterostructured solar cells, but the understanding of the mechanisms involved is still incomplete. In this work, it is shown that 2D/3D heterostructure are unstable under common thermal processing conditions, caused by the lattice expansion of strained 2D perovskite. Therefore an innovative fabrication technology involving a compressively strained PEA₂PbI₄ layer is proposed to compensate the internal tensile strain and stabilize the 2D/3D heterostructure. Moreover, a small amount of PEA⁺ diffusing into the grain boundaries of 3D perovskite forms 2D perovskite and passivates the defects there. Combining the effects of strain compensation and diffusion passivation, the stabilized 2D/3D perovskite solar cells deliver a reproducible and robust laboratory power conversion efficiency (PCE) of 21.31% for the p‐i‐n type devices, along with a high V _OC of 1.18 V. A certified PCE of 20.22% is confirmed by an independent national metrology institute.

In article number https://doi.org/10.1002/aenm.2020015672001567, Yu‐Ching Huang, Wei‐Fang Su, and co‐workers demonstrate a facile process for the mass‐production of perovskite solar cells. The process integrates slot‐die coating and near‐infrared irradiation heating techniques, combined with a new perovskite precursor formula to rapidly produce large‐area perovskite solar cells and modules in air.

A carbon‐encapsulated (Cs_0.15FA_0.85)Pb(I_0.9Br_0.1)₃ photocathode with a sandwich‐like structure is prepared and demonstrates state‐of‐the‐art performance for photo‐electrochemical (PEC) CO₂ reduction among organic–inorganic hybrid perovskite‐based PEC devices. A tandem device consisting of this photocathode and a Si photoanode further realizes unbiased PEC CO₂ reduction with an outstanding solar‐to‐CO energy conversion efficiency of 3.34%.

Abstract

Photo‐electrochemical (PEC) carbon dioxide reduction to chemicals or fuels has been regarded as an attractive strategy that can close the anthropogenic carbon cycle. However, identifying a PEC system capable of driving efficient and durable CO₂ conversion remains a critical challenge. Herein, the fabrication of a sandwich‐like organic–inorganic hybrid perovskite‐based photocathode with carbon encapsulation for PEC CO₂ reduction is reported. The carbon encapsulation not only affords protection to the perovskite, but also allows for efficient conductance of photogenerated electrons. When decorated with a cobalt phthalocyanine molecular catalyst, the photocathode shows an onset potential at 0.58 V versus reversible hydrogen electrode (RHE) and a high photocurrent density of −15.5 mA cm⁻² at −0.11 V versus RHE in CO₂‐saturated 0.5 m KHCO₃ under AM 1.5G illumination (100 mW cm⁻²), which represents state‐of‐the‐art performance in this field. Moreover, the photocathode remains stable during a continuous reaction that lasted for 25 h. Unbiased PEC CO₂ reduction is further realized by integrating the photocathode with an amorphous Si photoanode in tandem, delivering a solar‐to‐CO energy conversion efficiency of 3.34% and a total solar‐to‐fuel energy conversion efficiency of 3.85%.

Research on flexible mobile energy‐supply devices will promote the development of the Internet of Things. An embedded metal nickel (Ni)‐mesh transparent conductive electrode is used as a flexible substrate for perovskite solar cells (PSCs). These Ni‐mesh‐based PSCs exhibit excellent electric properties and remarkable environmental and mechanical stability.

Abstract

The rapid development of Internet of Things mobile terminals has accelerated the market's demand for portable mobile power supplies and flexible wearable devices. Here, an embedded metal‐mesh transparent conductive electrode (TCE) is prepared on poly(ethylene terephthalate) (PET) using a novel selective electrodeposition process combined with inverted film‐processing methods. This embedded nickel (Ni)‐mesh flexible TCE shows excellent photoelectric performance (sheet resistance of ≈0.2–0.5 Ω sq⁻¹ at high transmittance of ≈85–87%) and mechanical durability. The PET/Ni‐mesh/polymer poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS PH1000) hybrid electrode is used as a transparent electrode for perovskite solar cells (PSCs), which exhibit excellent electric properties and remarkable environmental and mechanical stability. A power conversion efficiency of 17.3% is obtained, which is the highest efficiency for a PSC based on flexible transparent metal electrodes to date. For perovskite crystals that require harsh growth conditions, their mechanical stability and environmental stability on flexible transparent embedded metal substrates are studied and improved. The resulting flexible device retains 76% of the original efficiency after 2000 bending cycles. The results of this work provide a step improvement in flexible PSCs.

A protonated amino silane coupling agent as an interlayer is exploited on rigid and flexible substrates, which not only sets up well‐matched growth underlay but also serves as a structural component of the lattice units, leading to less‐distorted perovskite films, resulting in an obvious advance in device performance, stability, and mechanical tolerance in the corresponding flexible device.

Abstract

Interface strains and lattice distortion are inevitable issues during perovskite crystallization. Silane as a coupling agent is a popular connector to enhance the compatibility between inorganic and organic materials in semiconductor devices. Herein, a protonated amine silane coupling agent (PASCA‐Br) interlayer between TiO₂ and perovskite layers is adopted to directionally grasp both of them by forming the structural component of a lattice unit. The pillowy alkyl ammonium bromide terminals at the upper side of the interlayer provide well‐matched growth sites for the perovskite, leading to mitigated interface strain and ensuing lattice distortion; meanwhile, its superior chemical compatibility presents an ideal effect on healing the under‐coordinated Pb atoms and halogen vacancies of bare perovskite crystals. The PASCA‐Br interlayer also serves as a mechanical buffer layer, inducing less cracked perovskite film when bending. The developed molecular‐level flexible interlayer provides a promising interfacial engineering for perovskite solar cells and their flexible application.

An aqueous‐solution‐processed cathode interlayer based on cost‐effective organosilica nanodots (OSiNDs) is demonstrated for organic solar cells (OSCs) with power conversion efficiency over 17% and excellent operational stability. The high photostability of OSiNDs‐based OSCs is attributed to the avoidance of photoinduced shunts and the photocatalytic effect, which are ineluctable shortcomings in inverted OSCs based on ZnO cathode interlayers.

Abstract

The performance and industrial viability of organic photovoltaics are strongly influenced by the functionality and stability of interface layers. Many of the interface materials most commonly used in the lab are limited in their operational stability or their materials cost and are frequently not transferred toward large‐scale production and industrial applications. In this work, an advanced aqueous‐solution‐processed cathode interface layer is demonstrated based on cost‐effective organosilica nanodots (OSiNDs) synthesized via a simple one‐step hydrothermal reaction. Compared to the interface layers optimized for inverted organic solar cells (i‐OSCs), the OSiNDs cathode interlayer shows improved charge carrier extraction and excellent operational stability for various model photoactive systems, achieving a remarkably high power conversion efficiency up to 17.15%. More importantly, the OSiNDs’ interlayer is extremely stable under thermal stress or photoillumination (UV and AM 1.5G) and undergoes no photochemical reaction with the photoactive materials used. As a result, the operational stability of inverted OSCs under continuous 1 sun illumination (AM 1.5G, 100 mW cm⁻²) is significantly improved by replacing the commonly used ZnO interlayer with OSiND‐based interfaces.

A biological polymer is employed to regulate the arrangement of SnO₂ nanocrystals on a substrate and induce vertical crystal growth of a perovskite layer on top. The enhanced interface contact between the electron transport layer and the perovskite layer significantly contributes to the improvement of efficiency and stability of derived planar perovskite solar cells.

Abstract

Perovskite solar cells (PSCs) have rapidly developed and achieved power conversion efficiencies of over 20% with diverse technical routes. Particularly, planar‐structured PSCs can be fabricated with low‐temperature (≤150 °C) solution‐based processes, which is energy efficient and compatible with flexible substrates. Here, the efficiency and stability of planar PSCs are enhanced by improving the interface contact between the SnO₂ electron‐transport layer (ETL) and the perovskite layer. A biological polymer (heparin potassium, HP) is introduced to regulate the arrangement of SnO₂ nanocrystals, and induce vertically aligned crystal growth of perovskites on top. Correspondingly, SnO₂–HP‐based devices can demonstrate an average efficiency of 23.03% on rigid substrates with enhanced open‐circuit voltage (V _OC) of 1.162 V and high reproducibility. Attributed to the strengthened interface binding, the devices obtain high operational stability, retaining 97% of their initial performance (power conversion efficiency, PCE > 22%) after 1000 h operation at their maximum power point under 1 sun illumination. Besides, the HP‐modified SnO₂ ETL exhibits promising potential for application in flexible and large‐area devices.

The first example of flexible transparent zinc‐mesh electrodes are demonstrated to assemble large‐scale Zn‐anode‐based electrochromic windows, and solar‐charging smart windows with sunlight‐intermittency issues perfectly addressed are presented. These findings facilitate new opportunities for the development of next‐generation transparent electrochemical devices.

Abstract

Newly born zinc‐anode‐based electrochromic devices (ZECDs), incorporating electrochromic and energy storage functions in a single transparent platform, represent the most promising technology for next‐generation transparent electronics. As the existing ZECDs are limited by opaque zinc anodes, the key focus should be on the development of transparent zinc anodes. Here, the first demonstration of a flexible transparent zinc‐mesh electrode is reported for a ZECD window that yields a remarkable electrochromic performance in an 80 cm² device, including rapid switching times (3.6 and 2.5 s for the coloration and bleaching processes, respectively), a high optical contrast (67.2%), and an excellent coloration efficiency (131.5 cm² C⁻¹). It is also demonstrated that such ZECDs are perfectly suited for solar‐charging smart windows as they inherently address the solar intermittency issue. These windows can be colored via solar charging during the day, and they can be bleached during the night by supplying electrical energy to electronic devices. The ZECD smart window platform can be scaled to a large area while retaining its excellent electrochromic characteristics. These findings represent a new technology for solar‐charging windows and open new opportunities for the development of next‐generation transparent batteries.

A series of new non‐fullerene acceptors (NFAs) with a large fused aromatic system are synthesized and used as electron‐trapping acceptors for realizing high‐performance photomultiplication‐type organic photodetectors (PM‐OPDs). The end‐functionalization of the extended fused‐ring NFA significantly affect the charge carrier lifetime of the resulting PM‐OPDs and preferentially focused acceptor distribution. Consequently, an unprecedentedly high external quantum efficiency over 150 000% is achieved.

Abstract

Photomultiplication‐type organic photodetectors (PM‐OPDs) with high external quantum efficiency (EQE) of over 100% are attracting increasing attention due to their potential importance in detecting weak incident light. Considering that the gain of PM‐OPD is determined by the ratio of carrier lifetime over carrier transit time, a systematic study on the effect of the end‐functionalization of a new extended aromatic fused‐ring non‐fullerene acceptor (NFA) on the carrier trap/transit time of the PM‐OPD. Photophysical analyses by means of ultraviolet‐visible absorption, ultraviolet photoelectron spectroscopy, and photoluminescence combined with structural analyses through grazing‐incidence wide‐angle X‐ray scattering show that fluorination of the NFA with the deepest lowest unoccupied molecular orbital level and non‐isotropic molecular ordering can yield the longest carrier lifetime. Furthermore, surface energy study show that fluorination of the NFA can also yield the most hydrophobic nature, which can allow the most efficient injection barrier thinning/lowering of the active layer/cathode interface under illumination due to the localized acceptor distribution toward cathode, maximizing the hole injection efficiency from cathode. As a result, an unprecedentedly high EQE of 156 000% is obtained from the optimized PM‐OPD. This work shows the importance of the molecular design of acceptor molecules in fabricating high‐performance PM‐OPDs.

In this work, a simple and low‐cost method to fabricate a stretchable and ultrathin skin‐inspired triboelectric nanogenerator (SI‐TENG) through synchronous electrospraying and electrospinning techniques is presented. Based on the optimized material selections and structure design, the SI‐TENG with the features of ultrathin, transparency, light‐weight, and excellent stretchability can be used as a self‐powered haptic sensor, such as game controllers.

Abstract

Accompanying the boom in multifunctional wearable electronics, flexible, sustainable, and wearable power sources are facing great challenges. Here, a stretchable, washable, and ultrathin skin‐inspired triboelectric nanogenerator (SI‐TENG) to harvest human motion energy and act as a highly sensitive self‐powered haptic sensor is reported. With the optimized material selections and structure design, the SI‐TENG is bestowed with some merits, such as stretchability (≈800%), ultrathin (≈89 µm), and light‐weight (≈0.23 g), which conformally attach on human skin without disturbing its contact. A stretchable composite electrode, which is formed by homogenously intertwining silver nanowires (AgNWs) with thermoplastic polyurethane (TPU) nanofiber networks, is fabricated through synchronous electrospinning of TPU and electrospraying of AgNWs. Based on the triboelectrification effect, the open‐circuit voltage, short‐circuit current, and power density of the SI‐TENG with a contact area of 2 × 2 cm² and an applied force of 8 N can reach 95 V, 0.3 µA, and 6 mW m⁻², respectively. By integrating the signal‐processing circuits, the SI‐TENG with excellent energy harvesting and self‐powered sensing capability is demonstrated as a haptic sensor array to detect human actions. The SI‐TENG exhibits extensive applications in the fields of human–machine interface and security systems.

In tandem organic photovoltaics, most ultraviolet–visible photons are absorbed by the front sub‐cell, so in the rear sub‐cell, excitons generated on large‐bandgap donors will be reduced significantly. This reduces the conductivity and limits the hole‐transporting property of the rear sub‐cell. An infrared‐absorbing polymer donor is introduced, which provides a second hole‐generation/transporting mechanism to minimize the aforementioned detrimental effects.

Abstract

In tandem organic photovoltaics, the front subcell is based on large‐bandgap materials, whereas the case of the rear subcell is more complicated. The rear subcell is generally composed of a narrow‐bandgap acceptor for infrared absorption but a large‐bandgap donor to realize a high open‐circuit voltage. Unfortunately, most of the ultraviolet–visible part of the photons are absorbed by the front subcell; as a result, in the rear subcell, the number of excitons generated on large‐bandgap donors will be reduced significantly. This reduces the (photo) conductivity and finally limits the hole‐transporting property of the rear subcell. In this work, a simple and effective way is proposed to resolve this critical issue. To ensure sufficient photogenerated holes in the rear subcell, a small amount of an infrared‐absorbing polymer donor as a third component is introduced, which provides a second hole‐generation and transporting mechanism to minimize the aforementioned detrimental effects. Finally, the short‐circuit current density of the two‐terminal tandem organic photovoltaic is significantly enhanced from 10.3 to 11.7 mA cm⁻² (while retaining the open‐circuit voltage and fill factor) to result in an enhanced power conversion efficiency of 15.1%.

A narrow‐bandgap polymer acceptor L14 with an acceptor–acceptor (A–A) backbone is synthesized, showing lower‐lying frontier molecular orbitals, higher electron mobility, and larger absorption coefficient without sacrificing photovoltage compared to its donor–acceptor (D–A) analog polymer, L11. When applied in all‐polymer solar cells, L14 yields an outstanding efficiency of 14.3%.

Abstract

Narrow‐bandgap polymer semiconductors are essential for advancing the development of organic solar cells. Here, a new narrow‐bandgap polymer acceptor L14, featuring an acceptor–acceptor (A–A) type backbone, is synthesized by copolymerizing a dibrominated fused‐ring electron acceptor (FREA) with distannylated bithiophene imide. Combining the advantages of both the FREA and the A–A polymer, L14 not only shows a narrow bandgap and high absorption coefficient, but also low‐lying frontier molecular orbital (FMO) levels. Such FMO levels yield improved electron transfer character, but unexpectedly, without sacrificing open‐circuit voltage (V _oc), which is attributed to a small nonradiative recombination loss (E _loss,nr) of 0.22 eV. Benefiting from the improved photocurrent along with the high fill factor and V _oc, an excellent efficiency of 14.3% is achieved, which is among the highest values for all‐polymer solar cells (all‐PSCs). The results demonstrate the superiority of narrow‐bandgap A–A type polymers for improving all‐PSC performance and pave a way toward developing high‐performance polymer acceptors for all‐PSCs.