Weak light absorption of graphene has limited the responsivity of graphene-based photodetectors. On the other hand, the slow response of PbSe as a mid-infrared range (MIR) detector makes this type of detector unsuitable as a commercial detector. Here, we report a fast MIR detector based on hybrid graphene-PbSe nanorods. For this purpose, a few-layer graphene piece was synthesized using a simple, scalable, and economical method on a cobalt layer, the synthesized graphene was transferred onto interdigitated copper electrodes, and then synthesized nanorods were spin coated on the transferred graphene. Strong and tunable light absorption in the quantum dot layer creates electric charges, which are transferred to the graphene, and due to the high charge mobility of graphene and long trapped-charge lifetimes in the quantum dot layer, they recirculate many times. The fabricated device has high speed and responsivity. The gain of fabricated detectors based on hybrid graphene quantum dots is 10.3 times more, their response time is 14.3 times faster, and their responsivity is 10 times more than conventional nanorod-based detectors. From the point of view of spectral selectivity, tuning the size of the nanorods helps optical detection from the IR to mid-IR.
This paper presents a concept to significantly improve the photocurrent of ultrathin crystalline silicon solar cells using plasmonic hemispherical dielectric-metal (core-shell) nanoparticles and backside gratings. The design of three-dimensional spherical and hemispherical arrays of nanoparticles on top of the surface of 0.8 μm crystalline silicon solar cells was simulated using finite-difference time-domain (FDTD) method. We used the FDTD results to investigate the photocurrent by solving the Poisson and drift diffusion equations. The results indicate an enhancement of between 80% and 93% in the photocurrent for cells with hemispherical Ag and Ag-SiO₂ core-shell nanoparticles, respectively, compared to a cell with spherical nanoparticles. In addition, for obtaining a higher photocurrent, triangular gratings were applied on the back side of the absorber and we obtained a photocurrent of 22 mA/cm². The simulated results indicate that the proposed structures increase the spectral response of thin-film crystalline silicon solar cells over a solar spectrum in the range of 400 nm-1200 nm. Finally, we investigated photocurrent as a function of incidence light angle and concluded that this approach is applicable to various thicknesses and shapes of nanoparticles.
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