All-polymer indoor photovoltaic modules

n-Type Conjugated Polymers Based on Double B←N Bridged Bipyridine Unit

ConspectusBoth p-type conjugated polymers and n-type conjugated polymers are required for organic optoelectronic devices, such as organic solar cells (OSCs), organic field-effect transistors (OFETs), organic thermoelectrics (OTEs), etc. The development of n-type conjugated polymers lags far behind that of the p-type counterparts in view of material diversity and optoelectronic device performance. This is mainly due to the lack of strong electron-withdrawing building blocks, which are always based on the imide unit. Double boron-nitrogen coordination bond (B←N) bridged bipyridine (BNBP), which was first developed in 2016, is an alternative kind of electron-withdrawing building block based on a B←N unit. BNBP itself possesses a planar and fixed configuration, low-lying electronic energy levels, strong fluorescence, and facile functionalization. A family of BNBP-based conjugated polymers has been developed. They show excellent and tunable optoelectronic properties, such as high electron mobility, low-lying and tunable lowest unoccupied molecular orbital (LUMO) energy level (ELUMO), medium bandgap, narrow absorption spectra in the visible range, high fluorescence quantum efficiency, etc. With rational molecular design of BNBP-based conjugated polymers, they have been widely used in organic optoelectronic devices with high performance, including OSCs, OFETs, and OTEs, indoor photovoltaics (IPVs), organic light-emitting diodes (OLEDs), organic photodetectors (OPDs), etc. Therefore, BNBP-based conjugated polymers have become an important class of optoelectronic materials. In this Account, we summarize the research progress on BNBP-based conjugated polymers.At first, we discuss BNBP itself, including its molecular design, synthesis, chemistry, and optoelectronic properties. Then we introduce the optoelectronic properties of BNBP-based conjugated polymers, including their light absorption property, fluorescence, electron mobility, and frontier electronic energy levels. We have systematically elucidated the relationship between the chemical structures, optoelectronic properties, and optoelectronic device performance of BNBP-based n-type conjugated polymers. The unique property of BNBP-based conjugated polymers is the high electron mobility in the amorphous state. Other noteworthy properties of these polymers are the medium bandgap and absorption spectra in the visible range. Next, we discuss the applications of BNBP-based conjugated polymers in OSCs, IPVs, OFETs, OTEs, OPDs, and OLEDs. The excellent optoelectronic device performance is noteworthy, such as power conversion efficiency (PCE) of 10% in OSCs, PCE of 26% in IPVs, electron mobility of 0.3 cm2 V-1 s-1 in OFETs, power factor of 25 μW m-1 K-2 in OTEs, specific detectivity of 1.79 × 1013 cm Hz1/2 W-1 in OPDs. Finally, we propose that great attention should be paid to the deep understanding of the electronic structures of BNBP itself and BNBP-based conjugated polymers as well as the new applications of BNBP-based conjugated polymers.

Precisely Controlling Polymer Acceptors with Weak Intramolecular Charge Transfer Effect and Superior Coplanarity for Efficient Indoor All-Polymer Solar Cells with over 27% Efficiency

Indoor photovoltaics (IPVs) are garnering increasing attention from both the academic and industrial communities due to the pressing demand of the ecosystem of Internet-of-Things. All-polymer solar cells (all-PSCs), emerging as a sub-type of organic photovoltaics, with the merits of great film-forming properties, remarkable morphological and light stability, hold great promise to simultaneously achieve high efficiency and long-term operation in IPV's application. However, the dearth of polymer acceptors with medium-bandgap has impeded the rapid development of indoor all-PSCs. Herein, a highly efficient medium-bandgap polymer acceptor (PYFO-V) is reported through the synergistic effects of side chain engineering and linkage modulation and applied for indoor all-PSCs operation. As a result, the PM6:PYFO-V-based indoor all-PSC yields the highest efficiency of 27.1% under LED light condition, marking the highest value for reported binary indoor all-PSCs to date. More importantly, the blade-coated devices using non-halogenated solvent (o-xylene) maintain an efficiency of over 23%, demonstrating the potential for industry-scale fabrication. This work not only highlights the importance of fine-tuning intramolecular charge transfer effect and intrachain coplanarity in developing high-performance medium-bandgap polymer acceptors but also provides a highly efficient strategy for indoor all-PSC application.

Optimizing Transport Carrier Free All-Polymer Solar Cells for Indoor Applications: TCAD Simulation under White LED Illumination

This work inspects the utilization of all-polymer solar cells (APSCs) in indoor applications under LED illumination, with a focus on boosting efficiency through simulation-based design. The study employs a SCAPS TCAD device simulator to investigate the performance of APSCs under white LED illumination at 1000 lux, with a power density of 0.305 mW/cm2. Initially, the simulator is validated against experimental results obtained from a fabricated cell utilizing CD1:PBN-21 as an absorber blend and PEDOT:PSS as a hole transportation layer (HTL), where the initial measured efficiency is 16.75%. The simulation study includes an examination of both inverted and conventional cell structures. In the conventional structure, where no electron transportation layer (ETL) is present, various materials are evaluated for their suitability as the HTL. NiO emerges as the most promising HTL material, demonstrating the potential to achieve an efficiency exceeding 27%. Conversely, in the inverted configuration without an HTL, the study explores different ETL materials to engineer the band alignment at the interface. Among the materials investigated, ZnS emerges as the optimal choice, recording an efficiency of approximately 33%. In order to reveal the efficiency limitations of these devices, the interface and bulk defects are concurrently investigated. The findings of this study underscore the significance of careful material selection and structural design in optimizing the performance of APSCs for indoor applications.

Indoor photovoltaic energy harvesting based on semiconducting π-conjugated polymers and oligomeric materials toward future IoT applications

With the advancement of artificial intelligence computing systems that can collect, analyze, and utilize metadata from our activities and surrounding environments, establishing self-powered electronic systems/networks supported by energy harvesters is strongly desired. With the lowering of power consumption in contemporary IoT electronics such as wireless sensors, indoor organic photovoltaic devices (iOPVs), which can be driven under ambient indoor light, have recently attracted significant interest as self-sustainable eco-friendly power sources. iOPVs based on organic semiconductors have unique advantages, such as light weight, flexibility, solution processability, and feasibility of low-temperature mass production. Additionally, the spectral tunability and high optical absorptivity of organic semiconductors make iOPVs more effective as energy harvesters in indoor lighting environments. With recent intensive research effort, iOPVs have realized the delivery of high power conversion efficiencies exceeding 25% with output power densities of several tens to a hundred μW cm−2, which are sufficient to drive various low-power electronics compatible with the IoT. This review article focuses on recent progress in iOPVs based on π-conjugated polymers and oligomeric materials and outlines their fundamental principles and characterization techniques.

Kirigami-inspired Automatically Self-inclining Bifacial Solar Cell Arrays to Enhance Energy Yield under Both Sunny and Cloudy Conditions

The application of photovoltaics (PVs) is expanding in various locations ranging from industrial facilities to residential housing. The emphasized concept in the PVs field is shifting from “watt-per-cost” to “energy-yield-per-watt.” To attain a high energy yield, fixed modules are not well suited to capture both direct and omnidirectional light. To achieve a high energy yield under both light conditions, we propose a self-inclining bifacial solar cell array fabricated by integrating a photothermal actuator, which senses incident light by itself, and actuating solar cells that incline at the appropriate angle to maximize captured light. In the vertical illumination state, the specific power of the self-inclining bifacial two-cell array is 11% higher than a fixed-angle aligned array. In an outside environment with a large proportion of diffused light, the self-inclining bifacial two-cell array also shows higher performance. We expect this work to enable PVs to be applied without regard to weather conditions.

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Proposing self-inclinable bifacial solar cell array depends on the weather condition

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It can automatically change its alignment angle using a photothermal actuator

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By self-incline at the appropriate angle, maximize captured light

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It shows better performance under predominantly diffused incident light

Domain size control in all-polymer solar cells

In all polymer solar cells (all-PSCs), the domain size is critical for device performance. In highly crystalline polymer blends, however, precisely adjusting the domain size remains a significant challenge because of the simultaneous crystallization of both components. Herein, a strategy that promotes acceptor and donor to crystallize separately was proposed. Take PBDB-T/N2200 blends for instance; the solution state and confined crystallization were combined, which induced the crystallization of N2200, and PBDB-T occurred during the film-forming process and at thermal annealing stage. This separated crystallization process lowers the driving force of phase separation without affecting the degree of crystallinity of the blends. Thus, an interpenetrating network with high crystallinity and proper domain size was obtained, which boosted the power conversion efficiency to 7.59%. Importantly, the relation between pre-aggregation and domain size was established, which may be a guide to precisely adjust the active layer’s domain size in all-PSCs.

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This strategy decreases domain size without sacrificing crystallinity

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A phase diagram about solution state and domain size was proposed