We demonstrate near-unity, broadband absorbing optoelectronic devices using sub-15 nm thick transition metal dichalcogenides (TMDCs) of molybdenum and tungsten as van der Waals semiconductor active ...layers. Specifically, we report that near-unity light absorption is possible in extremely thin (<15 nm) van der Waals semiconductor structures by coupling to strongly damped optical modes of semiconductor/metal heterostructures. We further fabricate Schottky junction devices using these highly absorbing heterostructures and characterize their optoelectronic performance. Our work addresses one of the key criteria to enable TMDCs as potential candidates to achieve high optoelectronic efficiency.
Typical thickness of the absorber layer in conventional thin film photovoltaics is of the order of few microns to few tens of nanometers depending upon the light absorber material used. Optimum ...values are often associated with the diffusion length of the minority charge carriers, that determine the upper limit and hence the optical absorption coefficient. On the other hand, it is desirable to increase absorption coefficient to maximize the utilization of incident photons. To achieve the same, the optical path length of the incident photons needs to be increased. Surface modifications via random/periodic texturing is considered for light trapping, as it induces multiple reflections of the incident photons, thereby increasing optical path length. In this work, glass substrates were textured with SU-8 2005 photoresist consisting of periodical array of micro cuboids (height ∼6 μm; side length ∼100/70/50/20μm) over an area of 20 mm × 20 mm using i-line lithography. Sb2Se3 absorber layer was conformally grown onto textured as well as on plain substrates via e-beam evaporation. UV–Vis-NIR spectra were recorded and the optical absorbance was analyzed as a function of cuboidal size. Optical absorption increases with decrease in the cuboidal feature size for side lengths up to 40μm and decreased for 20μm. Confirmative angle dependent specular reflectance study was done to correlate the observed absorption behavior, which was in corroboration with absorption measurements. Complementing absorption and reflectance results were understood through COMSOL Multiphysics optical path tracing simulations.
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•Sb2Se3 absorber layer is grown via e-beam on plain and SU8 2005 textured glass substrate.•Improved absorption is observed for all the feature sizes compared to plain absorber.•ADSR measurements were done for the optimization of the size of the feature.
•A hierarchical-structured downshifting film (QD-Hie) is designed to achieve highly-efficient photovoltaics (PVs).•QD-Hie film effectively manipulates the light-direction of both incident light and ...QD photoluminescence towards the PV direction.•Our films effectively improve the performance of both opaque and semi-transparent PVs via single-side and double-side attachment.•Unprecedented bifacial down-shifting layer of semi-transparent PV improve short-circuit current density (JSC) up to 25.97%.
Quantum dots (QDs) have been regarded as promising spectral converters for photovoltaic (PV) devices owing to their excellent photoluminescence (PL) characteristics. Herein, we report a highly-efficient QD hierarchical (QD-Hie) film that elevates the PV performance by integrating QDs with micro/nano hierarchical structures. The proposed film was designed to ensure low reflectance for incident light (air-to-device) and high reflectance for escape light (device-to-air), obtaining a light-trapping effect to increase the absorption of PVs at wide incident angles. The trapped ultraviolet photons in our film promoted the downshifting property of the QDs and amplified the generation of visible photons, thereby enhancing the PL characteristics of QDs up to 3.71 times with independency of the incidence angle. Furthermore, the hierarchical structure restricts the outward release of converted QDPL, ensuring high availability of the down-shifted photons to PVs. The optical benefit of our film was maximized by attaching them on both sides of bifacial semi-transparent dye-sensitized solar cells, resulting in the short-circuit current density (JSC) improvement of up to 25.97% under AM 1.5G illumination. Along with its high versatility and outstanding JSC increments, our study presents a new perspective of advanced spectral converting layers and provides practical viability for various optoelectronic devices.
In this study, a sensitive infrared photodetector (IRPD) composed of a germanium nanocones (GeNCs) array and PdSe2 multilayer is presented, which is obtained by a straightforward selenization ...approach. The as‐assembled PdSe2/GeNCs hybrid heterojunction exhibits obvious photovoltaic behavior to 1550 nm illumination, which renders the IRPD a self‐driven device without external power supply. Further device analysis reveals that the PdSe2/GeNCs hybrid based IRPD exhibits high sensitivity to 1350, 1550, and 1650 nm illumination with excellent stability and reproducibility. The responsivity and external quantum efficiency is as high as 530.2 mA W−1 and 42.4%, respectively. Such a relatively good device performance is related to the strong light trapping effect of GeNCs array, according to the theoretical simulation based on finite‐difference time‐domain. It is also found that the IRPD shows an abnormal sensitivity to IR illumination with a wavelength of 2200 nm. Finally, the present individual IRPD can also record the simple “F” image produced by 1550 nm, suggesting the promising application of the PdSe2/GeNCs hybrid device in future infrared optoelectronic systems.
A highly sensitive infrared light photo‐detector is fabricated by transferring multilayer PdSe2 on a germanium nanocones array with a strong light‐trapping effect. The as‐assembled PdSe2/GeNCs hybrid heterojunction devices can also record simple near‐infrared images.
UV light in solar spectra contributes to the generation of photocurrent but it has a negative influence on the stability of perovskite solar cells. To make better use of it, we demonstrate the ...reduction of UV light related negative effect without sacrificing power conversion efficiency by simultaneously introducing UV–visible downshifting and light trapping. Optimized perovskite solar cells can achieve a comparable efficiency over 21% to that of an unmodified device and enhanced UV stability due to UV–visible downshifting.
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The stability of perovskite solar cells is an important issue to be addressed for future applications. Perovskite solar cells are vulnerable to exposure to UV light due to promoted chemical reactions. However, preventing UV light from entering solar cells lowers the power conversion efficiency by reducing the photocurrent. The challenge is to improve UV stability without sacrificing efficiency. Here, we demonstrate the reduction of UV light-related negative effects from the perspective of spectral modification. By simultaneously introducing UV–visible downshifting and light trapping, perovskite solar cells can achieve a comparable efficiency of over 21% to that of an unmodified device. The optimized device obtains increased UV stability due to UV–visible downshifting. Different from other strategies, spectral modification externally alters the composition of incident light and improves UV stability without changing the internal device architecture, which is broadly applicable to perovskite solar cells with different structures. The present work may also find applications in other types of solar cells to boost the stability of devices exposed to UV light.
Two of the recent major research topics in optoelectronic devices are discussed: the development of new organic materials (both molecular and polymeric) for the active layer of organic optoelectronic ...devices (particularly organic light‐emitting diodes (OLEDs)), and light management, including light extraction for OLEDs and light trapping for organic solar cells (OSCs). In the first section, recent developments of phosphorescent transition metal complexes for OLEDs in the past 3–4 years are reviewed. The discussion is focused on the development of metal complexes based on iridium, platinum, and a few other transition metals. In the second part, different light‐management strategies in the design of OLEDs with improved light extraction, and of OSCs with improved light trapping is discussed.
The recent development of phosphorescent transition metal complexes for the fabrication of highly efficient and multicolored organic light‐emitting devices and the use of novel light‐management techniques to enhance the efficiency of light‐emitting and solar‐light‐harvesting devices are discussed.
With the aim of improving UV light trapping capability in monolayer graphene, a nanomesh metamaterial absorber is proposed, which exhibits the polarization-insensitive feature due to the geometrical ...symmetry. Through the functional combination of magnetic resonance and UV mirror, the absorption of unpolarized UV light in monolayer graphene can reach 99.5% under normal incidence. The absorption enhancement is induced by the magnetic resonance mode between the dielectric silica nanomesh and the calcium fluoride base layer. The effects of geometric parameters on the absorption spectra are systematically investigated. The proposed structure shows insensitive to manufacturing deviations, which can maintain at a high UV absorption rate of more than 99% within the nanomesh width ranging from 50 nm to 90 nm. Furthermore, after delicate optimization of the geometric parameters, two sharp resonances with absorbance more than 90% can be excited simultaneously inside the absorber. Our work provides an important theoretical guide for the design of optoelectronic devices based on two-dimensional materials in the UV range.
•Near-unity UV-light absorption is achieved in the monolayer graphene.•The proposed structure is insensitive to manufacturing deviations.•Two sharp resonances with absorbance over 90% can be excited inside the absorber.
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