High-efficient Schottky-junction silicon solar cell using silver nanowires covering nitrogen-doped amorphous carbon
Introduction
Two-dimensional (2D) carbon-based materials, such as graphene (Gr), graphene oxide (GO), and amorphous carbon (a-C), have received significant attention in a wide range of applications due to their excellent electrical, optical, mechanical properties, and chemical stability [[1], [2], [3], [4], [5], [6], [7]]. Recently, the 2D carbon-based materials have been proposed as potential electrodes for photocatalyst for H2 production, supercapacitor, lithium-ion battery, dye-sensitized solar cell (DSSC), and so on [[8], [9], [10], [11], [12], [13], [14]]. Particularly, the Gr was incorporated into silicon (Si)-based Schottky-junction structure for solar cell application as a transparent conducting electrode for charge separation and transport [[11], [12], [13], [14], [15], [16]]. In this Schottky-junction device, sunlight could easily penetrate the Gr layer and reach the Schottky-junction region. Consequently, the electron-hole pairs excited in Si were separated by the built-in electric field, which in turn leads to the generation of photocurrent [17]. Compared to the traditional p-n junction solar cells, the Schottky-junction solar cells lead to a new strategy for fabricating photovoltaic devices due to their inherent advantages such as low cost, simple fabrication, relatively high efficiency [17,18].
For the most of photovoltaic application, however, the synthesized Gr on metal substrate requires additional surface-to-surface transfer procedure to form Gr-on-silicon (Gr-Si) Schottky configuration. However, the transferred Gr on target substrate is often readily contaminated and mechanically damaged because of several wet chemical steps [19,20], which in turn results in the photovoltaic degradation of Gr-based Schottky devices that restricts further commercial application. Thus, there is a need for an alternative approach toward transfer-free graphene synthesized directly on Si substrate that is focusing on the homogenous formation of Schottky-contact without breaking of graphene film and trapping of impurities at the interface [21]. For instance, Kalita et al. reported the direct grown Gr on Si substrate by a solid phase reaction and the fabrication of Schottky-junction diode with power conversion efficiency (PCE) of 0.11% [22]. Heterojunction carbon-based solar cell was also studied by Adhikari and co-workers and showed a PCE up to 2.34% [23]. In particular, Ma and coworker have achieved the record PCE of 7.9% using a boron-doped diamond like a-C layer on a n-type silicon substrate [24]. Although the directly grown Gr or carbon-based materials that have a great potential to fabricate Schottky-junction solar cells, more studies are required to further enhance their photovoltaic performances.
This current issue has motivated us to develop a new Schottky configuration with high photovoltaic characteristics using directly deposited and annealed a-C thin film on n-Si substrate. Herein, we have prepared nitrogen (N)-doped a-C films by thermal annealing of N-containing as-deposited a-C films, and subsequently investigated the effect of annealing temperature on their electrical properties and photovoltaic performances. The results show that their electrical conductivities are gradually increased with increasing annealing temperature, which in turn leads to the improvement of the photovoltaic characteristics due to efficient charge separation and transport. Moreover, we first demonstrate the significant PCE enhancement of Schottky-junction solar cells constructed with silver nanowires (AgNWs) covering the 900 °C annealed N-doped a-C films (AgNWs-CN-900-Si). Specially, the series resistance of 0.2 wt% AgNWs-CN-900-Si solar cell with the sparsest AgNWs network is about 2.7 Ω, much lower than that of CN-900-Si solar cell with only Ag grid (as a control device). Consequently, the remarkable PCE of 6.17% is achieved on 0.2 wt% AgNWs-CN-900-Si solar cell, which is far superior to that of the control solar device (~0.13%). Furthermore, it is clarified that the 0.2 wt% AgNWs-CN-900-SiNWs solar cell shows the highest JSC of 23.42 mA/cm2 and PCE of 7.67%, more suitable for fabricating high-efficient AgNWs-coated Schottky-junction solar cells due to excellent light trapping at the surface and the enhancement of contact area.
Section snippets
Materials
Hydrogen fluoride (HF, 49%) and buffered oxide etchant (BOE, NH4F:HF = 6:1) were purchased from J. T. Baker® Chemicals. Silver nitrate (AgNO3, 99.1%), potassium hydroxide (KOH, 95.0%), ethyl alcohol (C2H5OH, 99.9%), and hydrogen peroxide (H2O2, 30%) were purchased from commercial suppliers. All chemicals were used without further purification. N-type Si (n-Si, 100, phosphorus density of ~2 × 1015 cm−3) wafer with a thickness of ~525 μm and resistivity of 1–10 Ω cm that was used as a n-type
Results and Discussion
N-containing a-C films were first deposited onto n-Si (100) substrates and subsequently annealed at 750, 800, 850, and 900 °C during 10 min under H2 atmosphere, aiming the application for Schottky-junction Si solar cells. Fig. 1a shows the Raman spectra for CN-as, CN-750, CN-800, CN-850, and CN-900 samples, respectively. The CN-as exhibits a broad band at around 1520 cm−1 that is deconvoluted into four-Gaussian bands centered at 1193.2, 1372.4, 1510.4, and 1586.3 cm−1, which are assigned to I
Conclusions
N-containing a-C films were first deposited onto various substrates and subsequently annealed at 750, 800, 850, and 900 °C during 10 min under H2 atmosphere, aiming the application for Schottky-junction Si solar cells. The resistance of N-doped a-C film gradually decreases with increasing annealing temperature, which in turn leads to the improvement of the photovoltaic characteristics. In response to increasing thermal annealing temperature, the open-circuit voltage (VOC), short-circuit current
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (2016R1A6A1A03012069).
References (58)
- et al.
Synthesis of ZnFe2O4/ZnO nanocomposites immobilized on graphene with enhanced photocatalytic activity under solar light irradiation
J. Alloys Compd.
(2013) - et al.
Graphite oxide–TiO2 nanocomposite and its efficient visible-light-driven photocatalytic hydrogen production
J. Alloys Compd.
(2012) - et al.
Self-assembly of NiO/graphene with three-dimension hierarchical structure as high performance electrode material for supercapacitors
J. Alloys Compd.
(2014) - et al.
Design and synthesis of porous nano-sized Sn@C/graphene electrode material with 3D carbon network for high-performance lithium-ion batteries
J. Alloys Compd.
(2014) - et al.
Improved photovoltaic performance of dye sensitized solar cell using ZnO–graphene nano-composites
J. Alloys Compd.
(2013) - et al.
Graphene/carbon nanotubes composites as a counter electrode for dye-sensitized solar cells
Curr. Appl. Phys.
(2012) - et al.
Ag-nanowires-doped graphene/Si Schottky-junction solar cells encapsulated with another graphene layer
Curr. Appl. Phys.
(2017) - et al.
Graphene transfer with reduced residue
Phys. Lett.
(2013) - et al.
High-ĸ dielectric oxide as an interfacial layer with enhanced photo-generation for Gr/Si solar cells
Carbon
(2017) - et al.
Boron-doped diamond-like amorphous carbon as photovoltaic films in solar cell
Sol. Energy Mater. Sol. Cell.
(2001)
Specific rare cell capture using micro-patterned silicon nanowire platform
Biosens. Bioelectron.
A simple and cost-effective approach for fabricating pyramids on crystalline silicon wafers
Sol. Energy Mater. Sol. Cell.
Transformation of nitrogen structures in carbonization of model compounds determined by XPS
Carbon
Characterization of amorphous and nanocrystalline carbon films
Mater. Chem. Phys.
Microstructure, mechanical and tribological properties of graphite-like amorphous carbon films prepared by unbalanced magnetron sputtering
Surf. Coating. Technol.
T.-i. Kim, Ultra-mechanically stable and transparent conductive electrodes using transferred grid of Ag nanowires on flexible substrate
Curr. Appl. Phys.
Electric field effect in atomically thin carbon films, science
Current saturation in zero-bandgap, top-gated graphene field-effect transistors
Nat. Nanotechnol.
Experimental observation of the quantum Hall effect and Berry's phase in graphene, nature
Intrinsic and extrinsic performance limits of graphene devices on SiO2
Nat. Nanotechnol.
Measurement of the elastic properties and intrinsic strength of monolayer graphene, science
Longitudinal unzipping of carbon nanotubes to form graphene nanoribbons
Nature
Graphene-based composites
Chem. Soc. Rev.
Graphene-on-silicon Schottky junction solar cells
Adv. Mater.
Chemically modulated graphene diodes
Nano Lett.
High-efficiency graphene/Si nanoarray Schottky junction solar cells via surface modification and graphene doping
J. Mater. Chem.
Work function engineering of graphene electrode via chemical doping
ACS Nano
Toward clean and crackless transfer of graphene
ACS Nano
Fabrication of a Schottky junction diode with direct growth graphene on silicon by a solid phase reaction
J. Phys. Appl. Phys.
Cited by (6)
Insights into the application of carbon materials in heterojunction solar cells
2023, Materials Science and Engineering R: ReportsCitation Excerpt :Subsequently, their corresponding HJSCs were first reported in 1996 [53], 1996 [99] and 2007[18]. The PCE of Si/a-C (3.8% in 1996 [53]) is further improved to 7.9% in 2001 [100] and 7.67% in 2021 [54]. The difficulty in rapidly improving their efficiency is attributed to its material properties of the disordered phase containing atoms in different hybridization states and a mixture of sp2 and sp3 sites[101], a severe recombination on the surface and inside may be caused by relatively high resistances of a-C films [54].
One-dimensional silver-titania nanocomposites as modification of photoanode for enhanced dye-sensitized solar cells – A review
2022, Materials Today: ProceedingsCitation Excerpt :However, the PCE of DSSCs is still low compared to other solar cells, so efforts are still needed to raise the efficiency of its energy conversion, including modification of the active material [6,7]. In recent years one-dimensional (1D) noble metals such as silver nanowires (AgNWs) have attracted attention as photoanode due to their increased light absorption and collection [8,9]. Therefore, many researchers have exploited its potential properties to be modified into nanocomposites with titanium dioxide (TiO2).