Solution Processed Semi-Transparent Organic Solar Cells Over 50% Visible Transmittance Enabled by Silver Nanowire Electrode with Sandwich Structure

Cyanobenzene-Modified Quinoxaline-Based Acceptors with Optimal Excitonic Behavior Enable Efficient Organic Solar Cells

Cyanogroup (-CN) is a strongly electron-withdrawing and highly polar functional group; therefore, cyanation has been extensively utilized to optimize the terminal groups of high-performance small-molecule acceptors (SMAs) in organic solar cells (OSCs). Herein, by regulating the cyanobenzene substitution in the central core for the first time, four novel SMAs are synthesized, named phCN-F, phCN-Cl, 2phCN-F, and 2phCN-Cl. Theoretical and experimental analyses have shown that asymmetric and symmetric cyanobenzene-substitution of the central core, coupled with selective terminal groups, can significantly affect the intrinsic excitonic properties of the molecule. Blends based on asymmetric cyanobenzene-substitution molecules possess tighter molecular packing and more suitable phase separation to facilitate exciton dissociation, charge transport, and charge extraction. The optimal device performance of the phCN-F-based OSC reaches 20.16%, which is significantly higher than that of symmetrically substituted OSCs. Furthermore, devices prepared based on phCN-F maintain over 90% of their initial efficiency after being heated at 85°C for 3000 h, demonstrating excellent thermal stability. This study elucidates the potential mechanisms for optimizing device performance through asymmetric cyanobenzene-substitution of the central core, providing valuable insights for the further design of record-breaking SMAs.

200 nm Ultrathin Freestanding Organic Photovoltaics

Ultrathin organic photovoltaics (OPVs) have great application prospects in the field of wearable electronics, such as electronic tattoos, electronic skins, etc. In this study, we report substrate-free ultrathin OPVs with a thickness of approximately 200 nm. The freestanding OPV devices achieve a power conversion efficiency of 11.6% and a power-per-weight ratio of 109.4 W g-1, with a weight of 1.06 g m-2. The ultrathin OPVs can self-adhere to various surfaces with complex and curved structures, ensuring excellent conformity. Notably, the ultrathin OPV devices demonstrate remarkable mechanical flexibility, maintaining 90% of their initial power conversion efficiency after 1000 compression-stretching cycles and are capable of bending to a radius of less than 2 μm. These attributes make ultrathin OPVs a crucial advancement in expanding the application landscape for wearable electronics and other special applications with ultraflexible and ultralight requests.

The art and science of translucent color organic solar cells

The artistic and scientific perspectives of the translucent color organic solar cells (OSCs), made with the emerging narrowband nonfullerene acceptors are explored. The translucent color OSCs, comprising a Fabry-Pérot microcavity optical coupling layer, have a power conversion efficiency of >15% and a maximum transparency of >20% for the three primary colors. The performance-color relationship of the translucent color OSCs is analyzed using a combination of high-throughput optical computing and experimental optimization, allowing light with desired color to pass through, while absorbing enough light to generate electricity. Replication of Piet Mondrian's artwork "Composition C (1920)" is demonstrated using a 10 × 10 cm2-sized translucent OSC module with a wide palette of colors and hues. The outcome of the work offers an opportunity for translucent color OSCs to function as both esthetic art and power generating windowpanes for use in our homes, offices, and even greenhouses.

Regulating Electron-Phonon Coupling by Solid Additive for Efficient Organic Solar Cells

Strong electron-phonon coupling can hinder exciton transport and induce undesirable non-radiative recombination, resulting in a shortened exciton diffusion distance and constrained exciton dissociation in organic solar cells (OSCs). Therefore, suppressing electron-phonon coupling is crucially important for achieveing high-performance OSCs. Here, we employ the solid additive to regulating electron-phonon coupling in OSCs. The planar configuration of SA1 confers a significant advantage in suppressing lattice vibrations in the active layers, reducing the scattering of excitons by phonons. Consequently, a slow but sustained hole transfer process is identified in the SA1-assisted film, indicating an enhancement in hole transfer efficiency. Prolonged exciton diffusion length and exciton lifetime are achieved in the blend film processed with SA1, attributed to a low non-radiative recombination rate and low energetic disorder for charge carrier transport. As a result, a high efficiency of 20 % was achieved for ternary device with a remarkable short-circuit current. This work highlights the important role of suppressing electron-phonon coupling in improving the photovoltaic performance of OSCs.

Designing a Highly Crystalline Polymer Donor with Alkylsilyl and Fluorine Substitution to Achieve Efficient Ternary Organic Solar Cells

Adopting a ternary strategy is an effective approach to enhance the power conversion efficiency (PCE) in organic solar cells (OSCs). Previous research on highly efficient ternary systems has predominantly focused on those based on highly crystalline dual small molecule acceptors. However, limited attention has been given to ternary systems utilizing dual polymer donors. Herein, by incorporating the fluorine and alkylsilyl substitution, a new polymer donor named PX1 is developed, which demonstrates strong crystallinity and excellent miscibility with polymer PM6. Moreover, PX1 broadens and enhances the absorption properties of the PM6:L8-BO blends, and its molecular orbital energy level is situated between those of PM6 and L8-BO, highlighting its suitability as a third component. Introducing 20% PX1 into the PM6:L8-BO system resulted in a high PCE of 18.82%. PX1 effectively suppresses charge recombination and reduces energy losses, while also serving as a morphology modulator that enhances the crystallization and improves the molecular packing order of the active layer by shortening the π-π stacking distance and extending crystalline coherence length. These factors collectively contribute to the performance improvements in ternary devices. This study demonstrates that employing a dual polymer donor strategy is a promising approach for achieving high-performance ternary OSCs.

Biobased Polymers Enabling the Synthesis of Ultralong Silver Nanowires and Other Nanostructures

Conventional polyol synthesis of silver nanowires has exclusively relied on polyvinylpyrrolidone (PVP), a nonbiodegradable polymer with no viable alternatives. The underlying reaction mechanism remains unclear. Herein, we discovered a new sustainable solution by employing biobased cellulose derivatives, including hydroxyethyl cellulose (HEC), as effective substitutes for PVP. Under mild reaction conditions (125 °C, ambient pressure), HEC facilitates the growth of ultralong silver nanowires (>100 μm) from penta-twinned silver seeds through a four-stage kinetic process. Theoretical calculations further reveal that HEC is physiosorbed onto the silver surfaces, while the presence of bromide ions (Br-) facilitates the evolution of seeds into nanowires. By varying halide ion concentrations and substitution in different cellulose derivatives, we successfully synthesized silver nanostructures with additional intriguing morphologies, including quasi-spherical nanoparticles, bipyramids, and nanocubes. Furthermore, transparent conductive films fabricated from ultralong silver nanowires synthesized with HEC demonstrated superior performance compared to those made with PVP-synthesized nanowires.

Molecular interaction induced dual fibrils towards organic solar cells with certified efficiency over 20

The nanoscale fibrillar morphology, featuring long-range structural order, provides abundant interfaces for efficient exciton dissociation and high-quality pathways for effective charge transport, is a promising morphology for high performance organic solar cells. Here, we synthesize a thiophene terminated non-fullerene acceptor, L8-ThCl, to induce the fibrillization of both polymer donor and host acceptor, that surpasses the 20% efficiency milestone of organic solar cells. After adding L8-ThCl, the original weak and less continuous nanofibrils of polymer donors, i.e. PM6 or D18, are well enlarged and refined, whilst the host acceptor L8-BO also assembles into nanofibrils with enhanced structural order. By adapting the layer-by-layer deposition method, the enhanced structural order can be retained to significantly boost the power conversion efficiency, with specific values of 19.4% and 20.1% for the PM6:L8-ThCl/L8-BO:L8-ThCl and D18:L8-ThCl/L8-BO:L8-ThCl devices, with the latter being certified 20.0%, which is the highest certified efficiency reported so far for single-junction organic solar cells.

Haze factor of silver nanowires in variable refractive index environment: experimental and simulation approaches

While silver nanowires (Ag NWs) have been demonstrated as a highly efficient transparent conducting material, they suffer from strong light scattering, which is quantified by a large haze factor (HF) in the optical spectrum. Here we investigate the influence of the dielectric environment on the light scattering of Ag NWs by comparing experimental measurements and simulations. In air, two peaks on the HF spectra are observed experimentally at the wavelength ofλI= 350 nm andλII= 380 nm and are attributed by simulations to the influence of the Ag NWs pentagonal shape on the localized surface plasmon resonance. The relative intensity between the two peaks is found to be dependent on whether the Ag NWs are in contact with the glass substrate or not. The HF behaviour in the near IR region seems to be dominated by Rayleigh scattering following simulations results. Dielectric environments of Ag NWs with various refractive indexes were obtained experimentally by the conformal deposition of different metal oxide coatings using atomic layer deposition, including Al-doped zinc oxide, Al2O3and SiO2coatings. The HF is found to be correlated with the refractive index environment in terms of HF peaks position, intensity and broadening. This trend of HF peaks is supported by a theoretical model to understand the optical mechanism behind this phenomenon.

Pressurized Back-Junction Doping via Spray-Coating Silver Nanowires Top Electrodes for Efficient Charge Collection in Bifacial Colloidal PbS Quantum Dot Solar Cells

Colloidal PbS quantum-dot solar cells (QDSCs) have long suffered from inefficient charge collection near the back-junction due to the lack of p-doping strategy, rendering their bifacial photovoltaic applications unsuccessful. Here, we report highly efficient photocarrier collection in bifacial colloidal PbS QDSCs by exploiting spray-coated silver nanowires (AgNWs) top electrodes. During our spray-coating process, pressurized Ag diffusion occurred toward the active layer, which induced effective p-doping and deep-level passivation. By manipulating the spray pressure, optimum AgNWs' stacking morphology enabling an appropriate level of Ag diffusion could be achieved, leading to Jsc over 30 mA/cm2 from the conventional n-i-p structure upon light illumination to the film side. The morphological and electrical behaviors of AgNWs according to the spray pressure are comprehensively explained in relation to the device performance. Finally, 50 bifacial cells were fabricated over 49 cm2 sized glass substrate, demonstrating the large-area processability and functionality of the spray-coated AgNWs with the effective back-junction engineering.