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The recent development of 2D monolayer lateral semiconductor has created new paradigm to develop p-n heterojunctions. Albeit, the growth methods of these heterostructures typically result in alloy structures at the interface, limiting the development for high-efficiency photovoltaic (PV) devices. Here, the PV properties of sequentially grown alloy-free 2D monolayer WSe2 -MoS2 lateral p-n heterojunction are explores. The PV devices show an extraordinary power conversion efficiency of 2.56% under AM 1.5G illumination. The large surface active area enables the full exposure of the depletion region, leading to excellent omnidirectional light harvesting characteristic with only 5% reduction of efficiency at incident angles up to 75°. Modeling studies demonstrate the PV devices comply with typical principles, increasing the feasibility for further development. Furthermore, the appropriate electrode-spacing design can lead to environment-independent PV properties. These robust PV properties deriving from the atomically sharp lateral p-n interface can help develop the next-generation photovoltaics.

Despite great improvements in traditional inorganic photodetectors and photovoltaics, more progress is needed in the detection/collection of light at low-level conditions. Traditional photodetectors tend to suffer from high noise when operated at room temperature; therefore, these devices require additional cooling systems to detect weak or dim light. Conventional solar cells also face the challenge of poor light-harvesting capabilities in hazy or cloudy weather. The real world features such varying levels of light, which makes it important to develop strategies that allow optical devices to function when conditions are less than optimal. In this work, we report an organic/inorganic hybrid device that consists of graphene quantum dot-modified poly(3,4-ethylenedioxythiophene) polystyrenesulfonate spin-coated on Si for the detection/harvest of weak light. The hybrid configuration provides the device with high responsivity and detectability, omnidirectional light trapping, and fast operation speed. To demonstrate the potential of this hybrid device in real world applications, we measured near-infrared light scattered through human tissue to demonstrate noninvasive oximetric photodetection as well as characterized the device's photovoltaic properties in outdoor (i.e., weather-dependent) and indoor weak light conditions. This organic/inorganic device configuration demonstrates a promising strategy for developing future high-performance low-light compatible photodetectors and photovoltaics.

By employing graphene quantum dots (GQDs), we have achieved a high efficiency of 16.55% in n-type Si heterojunction solar cells. The efficiency enhancement is based on the photon downconversion phenomenon of GQDs to make more photons absorbed in the depletion region for effective carrier separation, leading to the enhanced photovoltaic effect. The short circuit current and the fill factor are increased from 35.31 to 37.47 mA/cm(2) and 70.29% to 72.51%, respectively. The work demonstrated here holds the promise for incorporating graphene-based materials in commercially available solar devices for developing ultrahigh efficiency photovoltaic cells in the future.

A highly sensitive and selective nitrogen dioxide (NO2) sensor has been developed using reduced graphene oxide (rGO)/5-(4-Methoxycarbonylphenyl)-10,15,20-triphenyl-21H,23H-porphine (MCPTPP) composite. The rGO was prepared by thermal reduction of graphene oxide (GO), which was synthesized via an improved Hummer’s method. Using a drop-casting technique, the rGO/MCPTPP composite was deposited on an Indium Tin Oxide (ITO) flexible electrode. Various rGO/MCPTPP composites were developed by varying MCPTPP concentrations. A range of characterization tools confirmed the successful synthesis of the materials. The rGO/MCPTPP_1:3 composite exhibited high sensitivity, rapid response, and a recovery time of 31s. and 81s. respectively when exposed to 250 ppm NO2 at room temperature (RT). The sensor demonstrated good repeatability, excellent 60-day stability, and linearity from 50 to 500 ppm of NO2 concentration. The developed flexible chemiresistive sensor displayed excellent selectivity for NO2 among all the tested gases. The significant enhancement in NO2 sensing performance is attributed to the synergistic effect between rGO and MCPTPP. This work highlights the potential of the rGO/MCPTPP composite for sensitive and selective chemiresistive detection of NO2, making it promising for environmental monitoring and chemical industry applications. [ABSTRACT FROM AUTHOR]

In the current study, a chemiresistive SO2 sensor based on a composite of reduced graphene oxide (rGO) and 5, 10, 15, 20-tetra-p-tolyl-21H, 23H-porphine (TPTP) was developed and extensively studied. Improved Hummers methods were used to synthesize graphene oxide (GO), and a thermally heating bottom-up approach was used to reduce GO to rGO. Gold electrodes were thermally coated on the transparent sheet using a thermal evaporator. The composite of rGO/TPTP was synthesized using a simple chemical method. Structural, morphological, spectroscopic, electrical, and optical studies were carried out using X-ray diffraction, atomic force microscopy, field emission scanning electron microscopy, Fourier-transfer infrared spectroscopy, Raman spectroscopy, current–voltage, and UV–vis spectroscopy, respectively. The sensing response of rGO/TPTP for various concentrations of sulfur dioxide (SO2) was investigated in chemiresistive modality. The rGO/TPTP composite chemiresistive sensor displayed exceptional performance, with a consistent response spanning 1 ppm to 10 ppm. It exhibited outstanding repeatability, linearity, stability, and boasted an impressive limit of detection (LOD) of 1 ppm. This LOD is significantly lower than the recommended permissible exposure limit (PEL) of 5 ppm set by OSHA (Occupational Safety and Health Administration), USA. The sensor based on the rGO/TPTP composite exhibited a very fast response and recovery time of 33 s. and 27 s. respectively. [ABSTRACT FROM AUTHOR]