Graphene/Si Schottky solar cells: a review of recent advances and prospects

Abstract

Graphene has attracted tremendous interest due to its unique physical and chemical properties. The atomic thickness, high carrier mobility and transparency make graphene an ideal electrode material which can be applied to various optoelectronic devices such as solar cells, light-emitting diodes and photodetectors. In recent years, there has been a growing interest in developing graphene/silicon Schottky junction solar cells and the power conversion efficiency has reached up to 15.8% with an incredible speed. In this review, we introduce the structure and mechanism of graphene/silicon solar cells briefly, and then summarize several key strategies to improve the performance of the cells. Finally, the challenges and prospects of graphene/silicon solar cells are discussed in the development of the devices in detail.

Fig. 1. Characterizations of the graphene/n-Si Schottky junction. (a) Schematic illustration of the device configuration. (b) Energy diagram of the forward-biased graphene/n-Si Schottky junction upon illumination. Reproduced from with permission from Wiley.

Fig. 2. (a) Schematic illustration of the vapor doping process. The device was exposed to the SOCl₂ (or HNO₃) vapor for a few seconds and chlorine (nitrate) anions were doped on the films. (b) Scheme of the doping mechanism. (c) J–V characteristics of the solar cell before (red curve) and after (black) infiltration of dilute SOCl₂. (d) Light J–V curves and PCE of solar cells before and after volatile oxidant treatment. (e) The band schematics at the MLG/Si interface before and after doping. Reproduced from and with permission from The Royal Society of Chemistry.

Fig. 3. (a) J–V characteristics in the semi-logarithmic scale. (b) Amplified J–V characteristics of graphene/n-Si diodes. (c) The transmittance spectra of graphene. (a and b) Reproduced from with permission from The American Chemical Society (c) reproduced from with permission from IEEE Xplore.

Fig. 4. (a) SEM image of the surface of Au NPs/TFSA-doped graphene. The scale bar indicates 200 nm. (b) XPS spectra of graphene layers with and without Au NPs/TFSA dopants. (c) V_OC, (d) J_SC and FF, (e) PCE as functions of the Au thickness for both Au NPs/MLG/Si and Au NPs/FLG/Si solar cells. (f) Schematic diagrams of Pt-GWF/n-Si solar cell. (a and b) Reproduced from with permission from The Royal Society of Chemistry. (c–e) Reproduced from with permission from American Institute of Physics. (f) Reproduced from with permission from The Royal Society of Chemistry.

Fig. 5. (a) Current–voltage curves of solar cells based on graphene with 1, 2, 3, 4, 5, and 6 layers under illumination of 730 nm LED (2 mW cm⁻²). (b) The open-circuit voltage and short-circuit current of solar cells measured as functions of the number of graphene layers. (a and b) Reproduced from with permission from American Institute of Physics.

Fig. 6. Schematics diagrams of (a) graphene/planar Si and (b) graphene/SiNW junctions. (c) Schematic illustration of the graphene/SiHA Schottky junction solar cell. (d) Top-view SEM image of the graphene/SiHA device. (e) Photovoltaic characteristics and (f) EQE spectra of the graphene/SiHA Schottky junction solar cells with various hole depths. (a and b) Reproduced from with permission from The American Chemical Society. (c–f) Reproduced from with permission from The Royal Society of Chemistry.

Fig. 7. (a) Illustration of the TiO₂/graphene/Si structure (left) and cross-sectional SEM image showing a uniform TiO₂ coating (thickness of ∼65 nm) on top of the graphene–Si cell. (b) Schematic illustration of color graphene/Si heterojunction solar cells with double layer-MgF₂/ZnS films. Inset shows the SEM image of the Ag grid mesh. (c) J–V characteristics of an as fabricated graphene–Si solar cell, after HNO₃ vapor doping, and after TiO₂ coating (combined with HNO₃ doping), respectively. (d) Transmittance spectra of PMMA-removed and PMMA-coated (2000 rpm) graphene. The inset is a typical Raman spectrum of graphene on SiO₂/Si. Transmittance values at 550 nm are 96.0% and 97.4% for PMMA-coated and PMMA-removed samples, respectively. (e) J–V spectra of the devices with different structural colors measured under AM1.5, 100 mW cm⁻². J–V spectra of the devices without coating and with optimized anti-reflection coating were also presented for comparison. (a and c) Reproduced from with permission from The American Chemical Society. (b and e) Reproduced from with permission from Elsevier. (d) Reproduced from with permission from The Royal Society of Chemistry.

Fig. 8. (a) Schematic illustration of graphene/h-BN/Si solar cells. (b) Illuminated J–V characteristics of the graphene/Si solar cells with and without an h-BN interlayer. (c and d) Energy band diagrams of the graphene/Si Schottky junction solar cells without and with an h-BN electron blocking layer. Reproduced from with permission from Elsevier.