Limiting photovoltaic monochromatic light conversion efficiency

Notwithstanding the relatively low energy conversion efficiencies typical of standard solar photovoltaic systems, photovoltaic cells are shown, in principle, to be capable of converting well‐collimated monochromatic light at efficiencies arbitrarily close to 100%. To approach such efficiencies, radiative recombination must be the main recombination process within the cell. The intensity of the monochromatic light must be high, and the cell should be designed so that it does not absorb or emit light outside the range of angles and wavelengths required to accept the incident monochromatic light. The thermodynamic basis of such high efficiency is also briefly discussed. Copyright © 2001 John Wiley & Sons, Ltd.     

High‐Performance Hazy Silver Nanowire Transparent Electrodes through Diameter Tailoring for Semitransparent Photovoltaics

Solution‐processed metal nanowire networks have attracted substantial attention as clear transparent conductive electrodes (TCEs) to replace metal oxides for low‐cost and flexible touch panels and displays. While targeting photovoltaic applications, TCEs are expected to be more hazy for enhancing light absorption in the active layer, but are still required to retain high transmittance and low sheet resistance. Balancing these properties (haze, transmittance, and conductivity) in TCEs to realize high performance but high haze simultaneously is a challenge because they are mutually influenced. Here, by precisely tailoring the diameter of thick–long silver nanowires using rapid radial electrochemical etching, high hazy flexible TCEs are fabricated with high figure of merit of up to 741 (4 Ω sq^?1 at 88.4% transmittance with haze of 13.3%), surpassing those of commercialized brittle hazy metal oxides and exhibiting superiority for photovoltaic applications. Laminating such TCEs onto the perovskite solar cells as top electrodes, the obtained semitransparent devices exhibit power efficiencies up to 16.03% and 11.12% when illuminated from the bottom and top sides, respectively, outperforming reported results based on similar device architecture. This study provides a simple strategy for flexible and hazy TCEs fabrication, which is compatible with mild solution‐processed photovoltaic devices, especially those containing heat‐sensitive or chemical‐sensitive materials.     

Stretchable ITO-Free Organic Solar Cells with Intrinsic Anti-Reflection Substrate for High-Efficiency Outdoor and Indoor Energy Harvesting

Flexible photovoltaic devices are promising candidates for triggering the Internet of Things (IoT). However, the power conversion efficiencies (PCEs) of flexible organic photovoltaic (OPV) devices with high conductivity poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) electrodes on plastic are lagging behind the rigid devices due to the low transmittance of polyethylene terephthalate (PET)/PEDOT:PSS. Moreover, the poor stretchability of the commonly used plastic substrates largely hinders the practical application of wearable devices. Herein, a novel stretchable indium tin oxide (ITO)-free OPV device with a surface-texturing polydimethylsiloxane (PDMS) substrate for outdoor strong- and indoor dim-light energy harvesting is reported. The high diffuse transmittance and haze effect of the substrate enable stretchable ITO-free devices, yielding a high PCE of 15.3% under 1 sun illumination. More excitingly, the stretchable device based on textured PDMS/PEDOT:PSS maintains a comparable PCE of 20.5% (20.8% for the rigid device) under indoor light illumination. Notably, the stretchable device is much more insensitive to the light direction, maintaining 38.5% of the initial PCE at an extremely small incident angle of 10° (16.3% for glass/ITO-based counterpart). The texturing stretchable substrate provides a new direction for achieving high performance and enhanced light utilization for the stretchable light-harvesting device, suitable for indoor and outdoor applications.     

Self‐Powered Sensors Enabled by Wide‐Bandgap Perovskite Indoor Photovoltaic Cells

A new approach to ubiquitous sensing for indoor applications is presented, using low‐cost indoor perovskite photovoltaic cells as external power sources for backscatter sensors. Wide‐bandgap perovskite photovoltaic cells for indoor light energy harvesting are presented with the 1.63 and 1.84 eV devices that demonstrate efficiencies of 21% and 18.5%, respectively, under indoor compact fluorescent lighting, with a champion open‐circuit voltage of 0.95 V in a 1.84 eV cell under a light intensity of 0.16 mW cm^?2. Subsequently, a wireless temperature sensor self‐powered by a perovskite indoor light‐harvesting module is demonstrated. Three perovskite photovoltaic cells are connected in series to create a module that produces 14.5 µW output power under 0.16 mW cm^?2 of compact fluorescent illumination with an efficiency of 13.2%. This module is used as an external power source for a battery‐assisted radio‐frequency identification temperature sensor and demonstrates a read range by of 5.1 m while maintaining very high frequency measurements every 1.24 s. The combined indoor perovskite photovoltaic modules and backscatter radio‐frequency sensors are further discussed as a route to ubiquitous sensing in buildings given their potential to be manufactured in an integrated manner at very low cost, their lack of a need for battery replacement, and the high frequency data collection possible.     

聚合物光诱导电荷转移光电池的研究进展

综述了以共轭聚合物作为电子施主和 C6 0 及其衍生物作为电子受主的共混与多层器件结构的聚合物光诱导电荷转移光电池的研究进展。对这类新型结构的光电池的基本性能及机制作了介绍。低生产成本、能通过简单甩膜或印刷方式就能制备大面积器件的优势使聚合物光电池在许多实际应用领域具有广阔的前景。对今后进一步提高这类光电池的能量转换效率的研究方向进行了探讨     

Latest Progress on Photoabsorbent Materials for Multifunctional Semitransparent Organic Solar Cells

Semi-transparent organic solar cells (ST-OSCs) have revolutionized the field of photovoltaics (PVs) due to their unique abilities, such as transparency and color tunability, and have transformed normal power-harvesting OSC devices into multifunctional devices, such as building-integrated photovoltaics, agrivoltaics, floating photovoltaics, and wearable electronics. Very recently, ST-OSCs have seen remarkable progress, with a rapid increase in power conversion efficiency from below 7% to 12–14%, with an average visible transparency of 9–25%, especially due to the use of low bandgap semiconductors including polymer donors and non-fullerene acceptors that exhibit absorption in the near-infrared region as photoabsorbent materials. From this perspective, the latest developments in ST-OSCs stemming from the innovations in photovoltaic materials that delivered multifunctional ST-OSCs with top-of-the-line power conversion efficiencies are discussed to shed light on the structure-property relationship between molecular design and current challenges in this cutting-edge research field. Finally, personal perspectives, including research directions for the future use of ST-OSCs in multifunctional applications, are also proposed.     

Crown Ether-Assisted Growth and Scaling Up of FACsPbI3 Films for Efficient and Stable Perovskite Solar Modules

FACs-based (FA⁺, formamidinium and Cs⁺, cesium) perovskite solar cells have gained great attention due to their remarkable light and thermal stabilities toward practical application of perovskite modules. However, the moisture instability and difficulty in scalable fabrication are still the main obstacles blocking their photovoltaic applications in current status. Here, the employment of novel interaction between crown ether with metal cations is introduced to tailor the uniform growth and inhibit moisture invasion during the crystallization of α-phase FACsPbI₃, yielding the successful synthesis of high-quality perovskite films in a large scale. Consequently, perovskite solar cells (PSC) modules in the total area of 4 × 4 and 10 × 10 cm² are readily fabricated with respective champion efficiencies of 16.69% and 13.84% and excellent stability over 1000 h. This facile scaling-up strategy assisted by crown ether has shown great promise for pursuing efficient and highly stable large-area PSC modules.     

Polycrystalline silicon thin-film solar cells: The future for photovoltaics?

Based on performance, material availability, consumer acceptance, life expectancy, environmental considerations and the potential for low cost, thin-film polycrystalline silicon solar cells are well placed to have a significant impact in the future. of key importance will be the achievement of performance targets, because module efficiencies of at least 15% are probably necessary in the long term for photovoltaics to have a significant impact in grid-connected applications. Strategies for achieving these performance levels with mediocre material quality and only moderate surface passivation and light trapping are presented. the challenges associated with the supporting substrate choice and layer depostion techniques and structures are discussed and the psesent practices reviewed. Important considerations include device performance, cost, throughput, device area and simplicity of fabrication and operation. Promising efficiencies in the vicinity of 15% have already been demonstrated using a number of different crystalline silicon layer-formation techniques. Novel device structures based on incorporation of narrow bandgap materials (Si/Ge alloys) or defect layers, quantum wells and the impurity photovoltaic effect are considered, with particular emphasis given to approaches that compensate for the current loss in thin-film cells. It appears increasingly likely that polycrystalline silicon thin-film solar cells will have an impact on the development of photovoltaics in the future and may in fact provide the means for the substantial cost reductions necessary for significant penetration into utility markets.     

＞35％ 5-junction space solar cells based on the direct bonding technique

Multijunction solar cells are the highest efficiency photovoltaic devices yet demonstrated for both space and terrestri-al applications.In recent years five-junction cells based on the direct semiconductor bonding technique (SBT),demonstrates space efficiencies ＞35％ and presents application potentials.In this paper,the major challenges for fabricating SBT 5J cells and their appropriate strategies involving structure tunning,band engineering and material tailoring are stated,and 4-cm235.4％(AM0,one sun) 5J SBT cells are presented.Further efforts on detailed optical managements are required to improve the cur-rent generating and matching in subcells,to achieve efficiencies 36％-37％,or above.     

Plasmonic‐Induced Photon Recycling in Metal Halide Perovskite Solar Cells

Organic–inorganic metal halide perovskite solar cells have emerged in the past few years to promise highly efficient photovoltaic devices at low costs. Here, temperature‐sensitive core–shell Ag@TiO₂ nanoparticles are successfully incorporated into perovskite solar cells through a low‐temperature processing route, boosting the measured device efficiencies up to 16.3%. Experimental evidence is shown and a theoretical model is developed which predicts that the presence of highly polarizable nanoparticles enhances the radiative decay of excitons and increases the reabsorption of emitted radiation, representing a novel photon recycling scheme. The work elucidates the complicated subtle interactions between light and matter in plasmonic photovoltaic composites. Photonic and plasmonic schemes such as this may help to move highly efficient perovskite solar cells closer to the theoretical limiting efficiencies.     

Polyterthiophenes as Donors for Polymer Solar Cells

Thiophene‐containing polymers blended with fullerenes have recently demonstrated impressively high photovoltaic efficiencies. One drawback of this class of polymers is their relatively low ionization potential, which leads to rather low open‐circuit voltages. Polyterthiophenes belong to a material class that has recently captured a large amount of interest for polymer electronic applications because of its excellent transport properties. Because of the slightly lower ionization potential, this material class appears more attractive for photovoltaic applications than polythiophenes. In this work, the photovoltaic performance of bulk heterojunction solar cells from polyterthiophene/fullerene composites is discussed and compared to the polymer/fullerene blend morphology.     

A Novel Silicon Photovoltaic Cell Using a Low-Temperature Quasi-Epitaxial Silicon Emitter

A new silicon solar cell fabricated using a low-temperature process is demonstrated with a highly conductive (n+) quasi-epitaxial (qEpi-Si) silicon emitter deposited on silicon substrates, without using transparent conductive oxides. The emitter was formed by a plasma-enhanced chemical vapor deposition process on granular multicrystalline silicon (mc-Si) substrates at a substrate temperature of 250 . The new qEpi-Si/(p)mc-Si junction was found to be of good quality for photovoltaic applications. Solar cells of 1- area and conversion efficiencies exceeding 10% have been fabricated in a simple fabrication process and device structure.     

Upconversion effects on the performance of near-infrared laser-driven polymer photovoltaic devices

We have explored the upconversion (UC) effects resulting from the presence of NaYF₄:Yb/Er nanocrystals in near-infrared laser-driven organic photovoltaic devices (OPVs). Illumination of these UC nanomaterials with monochromatic light (980 nm) led to emission of visible light, which was subsequently absorbed by the polymer photoactive layer. We infer that both the long-wavelength charge-transfer absorption of the polymer blend and the UC effect contributed to the obvious near-infrared photovoltaic response. The resulting UC effects led to noticeable enhancements in the photocurrent and the efficiencies of the OPV devices under illumination at 980 nm.     

Recent progress in thin-film cadmium telluride solar cells

Cadmium telluride (CdTe) with a room-temperature bandgap energy of 1.45 eV has been shown to be the most promising low-cost, thin-film photovoltaic material for terrestrial applications. Significant progress has been made during the past several years, and thin-film CdTe solar cells of > 1 cm² area with conversion efficiencies higher than 12% have been prepared by several techniques. Thin-film CdTe photovoltaic modules with 10% efficiency have also been produced. They are of the heterojuntion configuration using a transparent conducting semiconductor (TCS) as the window and p-CdTe as the absorber. In this paper, the potential window materials for thin-film CdTe solar cells are discussed. Thus far, cadmium sulphide (CdS) with a bandgap energy of 2.42 eV at room temperature has been found to be best suited for efficient CdTe solar cells. the deposition techniques for p-CdTe films capable of producing efficient solar cells, including close-spaced sublimation (CSS), electrodeposition, screen printing and spraying, are briefly reviewed, and the characteristics of the resulting solar cells are discussed. It is concluded that the efficiency of thin-film CdTe solar cells can be increased to 18-19% in the near-term, leading to 15-16.5% efficient modules.     

Weakly Conjugated Hybrid Zinc Porphyrin Sensitizers for Solid‐State Dye‐Sensitized Solar Cells

Molecularly engineered weakly conjugated hybrid porphyrin systems are presented as efficient sensitizers for solid‐state dye‐sensitized solar cells. By incorporating the quinolizino acridine and triazatruxene based unit as the secondary light‐harvester as well as electron‐donating group at the meso‐position of the porphyrin core, the power conversion efficiencies of 4.5% and 5.1% are demonstrated in the solid‐state devices containing 2,2′,7,7′‐tetrakis (N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spiro bifluorene as hole transporting material. The photovoltaic performance of the triazatruxene donor based porphyrin sensitizer is better than that of the previously published porphyrin molecules exhibiting strongly conjugated push–pull structure. The effect of molecular structure on the optical and electrochemical properties, the dynamics of charge extraction, as well as the photovoltaic performance are systematically investigated, which offers a new design strategy for further refinement of porphyrin molecules.     

Photostrictive actuators

Photostrictive materials, exhibiting light induced strain, are of interest for future generation wireless remote control photo-actuators, micro-actuators, and micro-sensors applications. (Pb, La)(Zr, Ti) O₃ (PLZT) ceramics doped with WO₃ exhibit large photostriction under uniform illumination of near-ultraviolet light. Using a bimorph configuration, a photo-driven relay and a micro walking device have been demonstrated. However, for the fabrication of these devices, materials exhibiting higher photovoltaic effect and higher response speed must be developed. The present paper reviews a new theoretical model for photovoltaic effect first, then enhanced performance photostrictive materials through sample surface characteristics, finally its potential future applications.     

Evaluation of mismatch and non‐uniform illumination losses in monolithically series‐connected GaAs photovoltaic converters

This work evaluates the influence of mismatch illumination on the performance of GaAs monolithically series‐connected photovoltaic converters under laser illumination. A theoretical model which takes into account nonuniform illumination, light spillage and mismatch losses is presented. The influence of laser spot size on the converter efficiency is also addressed. The laser spot size must be chosen in order to make a trade‐off between mismatch and nonuniform illumination losses, which predominate in a laser spot diameter smaller than the diameter of the device, and spillage losses, which predominate in a laser spot diameter larger than that of the device. For single photovoltaic converters, it is advisable to reduce the laser spot diameter to values to less than that of the converter. For multiple photovoltaic converters, especially if there is a considerable misalignment between the light source and the device, a spot diameter slightly larger than that of the device is recommended. Otherwise, mismatch losses could severely limit MPC performance. When the laser beam diameter equals the device diameter, and for a 5% misalignment, efficiencies of 55.0, 53.6 and 50.1% are envisaged, for two‐, three‐ and six‐sector multiple photovoltaic converters, respectively. Copyright © 2002 John Wiley & Sons, Ltd.     

Research opportunities in crystalline III–V photovoltaics

Although III-V solar cells have been developed to a high level of performance, opportunities for fundamental advances still exist. For example, new structures could lead to substantial gains in conversion efficiency, multi-junction solar cells could achieve efficiencies well above 50%, and new materials could be developed for applications such as thermophotovoltaics. In this paper, the authors describe research opportunities that could provide the scientific base for substantial enhancements in the performance of crystalline III-V photovoltaic cells.     

Polymer Photovoltaic Devices Employing a Chemically Fixed p–i–n Junction

Polymer photovoltaic devices commonly suffer from low power conversion efficiencies despite the potential for much higher performance. Here we apply a recently reported system for creating a chemically fixed polymer p‐i‐n junction to polymer photovoltaic devices. Both single‐component and blended donor/acceptor devices are fabricated and tested. We study the devices during charging and find that the changes in light and dark current characteristics are consistent with the formation of a p‐i‐n junction in the active material. While the overall performance of these systems need improvement, the devices show promising open circuit voltages, suggesting the possibility for improving the state‐of‐the‐art in polymer photovoltaic techno logies with continued materials development.     

Metal-free photosensitizers based on benzodithienothiophene as π-conjugated spacer for dye-sensitized solar cells

A novel series of metal-free organic photosensitizers based on D-π-A or D-A₁-π-A structure motif namely, BD-n, (where n = 1–5) bearing a high hole-transporting benzodithienothiophene as the π-bridge for the first time, carbazole or triarylamine as the electron-donor and benzothiadiazole or quinoxaline as the auxiliary electron-deficient unit was synthesized and investigated for DSSC applications. DSSCs based on these five photosensitizers were also fabricated which exhibited efficiencies ranging from 3.92% to 5.46%. Among these DSSCs, devices based on D-A₁-π-A type dye, BD-3 and bidenate dye, BD-5 as a photosensitizer afforded the best efficiencies of 5.34%–5.46%. Our results suggested that an incorporation of a proper auxiliary accepting group (A₁) into the D-π-A conjugation system to enhance light harvesting and charge transfer as well as the use of V-shaped di-anchoring strategy to suppress aggregation on the TiO₂ surface were found to be useful and effective strategies to enhance the photovoltaic performance of a DSSC. These devices exhibited relatively long electron lifetimes suggesting the slow charge recombination kinetics and thus better DSSC performance. Our findings also suggest that benzodithienothiophene is a promising π-bridge to construct organic photosensitizers for high-efficiency DSSCs.