Enhanced photovoltaic performances of graphene/Si solar cells by insertion of a MoS₂thin film

Abstract

This layer functions as an effective passivation and electron-blocking/hole-transporting layer.We also demonstrated that the photovoltaic properties are enhanced with increasing number of graphene layers and decreasing thickness of the MoS 2 layer. A high photovoltaic conversion efficiency of 11.1% was achieved with the optimized trilayer-graphene/MoS 2 /n-Si solar cell.Keywords: solar cell, molybdenum disulfide (MoS 2 ), two-dimensional material, graphene, Schottky junction TEXTWith an increase in low dimensional material research, these atomically thin materials have been widely and intensively studied from the viewpoints of both fundamental physics and applications. [1][2][3][4][5][6][7][8] Transition-metal dichalcogenides (TMDs) (MX 2 ; M = Mo, W; X = Se, S) are among the most attractive two-dimensional (2D) layered materials that can be thinned down to atomic-scale thickness. 9 Monolayer molybdenum disulfide (MoS 2 ), which is a typical and wellstudied TMD system, is a direct bandgap semiconductor, whereas bulk MoS 2 is an indirect bandgap semiconductor. The direct-to-indirect energy-gap transition occurs in MoS 2 when it changes from a monolayer to a bilayer, and the optical bandgap changes from 1.8 eV in [23][24][25][26] In the case of graphene/Si solar cell, the approaches used to improve photovoltaic performance have primarily involved carrier doping in the graphene layer, the insertion of a oxide layer, or the deposition of an antireflection layer onto the surface of a solar cell. [27][28][29][30][31][32][33] In this study, we investigate the photovoltaic properties of graphene/MoS 2 /n-Si solar cells. The photovoltaic properties were considerably enhanced by the insertion of chemical vapor deposition (CVD)-grown large MoS 2 thin film, which functions as an effective passivation and electron-blocking/hole-transporting layer. The optimized graphene/MoS 2 /n-Si solar cell exhibited a high photovoltaic conversion efficiency of 11.1%, which is a remarkable conversion efficiency in a photovoltaic device using MoS 2 thin film. RESULTS AND DISCUSSIONFigure 1(a) shows a schematic of the graphene/MoS 2 /n-Si solar cell. sulfur was also heated to 190 °C using a ribbon heater, resulting in sulfur transport. All processes were performed under high-purity Ar gas flow flowing at 50 sccm under ambient conditions. We fabricated MoS 2 films with various thicknesses on SiO 2 /Si substrates, as shown in Figure S1.The graphene/MoS 2 /n-Si solar cells were fabricated by transferring CVD-grown MoS 2 films and graphene films (single-layer graphene, Graphene Platform) onto the n-type Si substrate (1-5 cm −1 ) with an ~300-nm-thick SiO 2 layer. A circular window with a diameter of 1 mm was patterned on the SiO 2 /Si substrate. This Si substrate was dipped into buffered hydrofluoric acid (HF) solutions for several seconds to remove the natural oxidation layer on the window, which obstructs the electrical contact. The MoS 2 film was then transferred via thermal release tape (REVALPHA; No. 3195MS, Nitto Denko). In this study, ...

Exciton formation assisted by longitudinal optical phonons in monolayer transition metal dichalcogenides

“…Due to the comparatively higher Fröhlich interaction strengths and lower LO phonon energies of monolayer MoSe 2 and WSe 2 , the exciton formation times of the selenidebased dichalcogenides are smaller than the sulphide-based dichalcogenides at T e = T h = T ex = 100 K and 300 K (with | K| ≤ 0.05 × 10 10 m −1 ). The results of this study is expected to be useful in understanding the role of the exciton formation process in electroluminescence studies [46,82] and exciton-mediated processes in photovoltaic devices [31,33,83].…”

Molybdenum Disulphide Heterointerfaces as Potential Materials for Solar Cells, Energy Storage, and Hydrogen Evolution

“…The optimum efficiency has been observed for trilayer graphene/MoS 2 /n‐Si junctions, as shown in Figure c. The observed characteristics were clearly explained based on the energy band diagram of these junctions, which is shown in Figure d . Similar work has been done using MoS 2 as an electron transport layer in graphene/Si solar cells; here, the effect of annealing temperature and film thickness of MoS 2 was studied in detail.…”

Graphene‐Based Mixed‐Dimensional van der Waals Heterostructures for Advanced Optoelectronics

“…The average power conversion efficiency (PCE) of the unoptimized cells is ≈1.5%, which is much lower than the theoretical value ( Figure a) . The next optimization efforts for improving the PCE of such heterojunctions mainly include patterning Si pillar array to increase the light absorption (Figure b), doping of graphene to modulate its work function and carrier density, Si surface passivation, insertion of electron‐blocking/hole‐transporting layer, antireflection coating, and graphene layer number control . Maximized PCE of GR‐Si solar cells over 15% has been achieved after the above collaborative optimizations (Figure c) .…”