COMMUNICATION © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim (1 of 5) 1600822 wileyonlinelibrary.com Stable 16.2% Efficient Surface Plasmon-Enhanced Graphene/GaAs Heterostructure Solar Cell Shi-Sheng Lin,* Zhi-Qian Wu, Xiao-Qiang Li, Yue-Jiao Zhang, Sheng-Jiao Zhang, Peng Wang, Rajapandiyan Panneerselvam, and Jian-Feng Li* Prof. S.-S. Lin, Z.-Q. Wu, Dr. X.-Q. Li, S.-J. Zhang, Dr. P. Wang College of Microelectronics Department of Information Science and Electronic Engineering Zhejiang University Hangzhou 310027, P. R. China E-mail: shishenglin@zju.edu.cn Prof. S.-S. Lin State Key Laboratory of Modern Optical Instrumentation Zhejiang University Hangzhou 310027, P. R. China Y.-J. Zhang, Dr. R. Panneerselvam, Prof. J.-F. Li State Key Laboratory of Physical Chemistry of Solid Surfaces and College of Chemistry and Chemical Engineering Xiamen University Xia-men 361005, P. R. China E-mail: li@xmu.edu.cn DOI: 10.1002/aenm.201600822 conversion, although rarely explored for the graphene/semi- conductor heterostructure. Metallic nanoparticles (NPs) based surface plasmon resonance has been reported to improve the performance of solar cells based on near field concentra- tion. [21–23] The resonance wavelength of the incident light can be tuned by changing the size and shape of the metallic NPs. It has been reported that a considerable efficiency enhance- ment of Si, [24] dye-sensitized, [25,26] and organic solar cells [27] is possible for future applications. This efficiency enhancement is generally attributed to increased light absorption in the photo- active layer. [28–30] To fully utilize the near field concentration, the metallic NPs should be placed near the photoactive layer, where the electron–hole pairs are generated and collected. The shallow junction in a graphene/semiconductor heterostructure-based solar cell naturally forms a platform for utilizing the surface plasmon physics. Herein, we use Au NPs to improve the performance of gra- phene/GaAs heterostructure solar cells. Significantly, PCE is increased from 8.83% to 11.8%, mainly induced by the short circuit current increased from 19.1 to 24.9 mA cm -2 . With chemical doping and antireflection coating, PCE has been fur- ther improved to 16.2%. These results prove that the concentra- tion of incident light in the vertical direction is an appropriate way to enhance the performance of solar cells by generating carriers near the front junction. With chemical vapor deposition (CVD) technique, growth of graphene on copper foils was carried out at 1000 °C for 60 min with reaction source flux ratio of CH 4 :H 2 equals to 3:1. [12] The synthesis processes of the Au NPs can be found in the Note S1 (Supporting Information). The obtained Au NPs were finally diluted in ethanol with a desired particle concentration. Thin film n-type GaAs with a thickness of 2 μm was grown with metal organic CVD at 400 °C on n-type GaAs wafer with n-type interlayer of AlGaAs (1 μm). The doping concentration of the GaAs wafer, AlGaAs layer, and top thin GaAs layer are about 1 × 10 18 , 1 × 10 18 , and 5 × 10 17 cm -3 , respectively. Rear Au contact with a thickness of 60 nm was thermally evapo- rated on the back surface of GaAs wafer. SiN x dielectric layer with a thickness of 80 nm was deposited on the front surface of top thin layer of GaAs with lithography-processed mask using plasma-enhanced CVD and used as an insulating layer under the graphene/metal contact. The open window in SiN x film defined the active area (10 mm × 1 mm) of graphene/ GaAs solar cell. Prior to transferring graphene onto GaAs sur- face, the open area was cleaned by dipping the samples into 10 wt% HCl solution for 5 min followed with DI water rinse. Graphene was transferred onto the GaAs substrate using poly- methyl methacrylate (PMMA) as the supporting layer. Then The discovery of graphene opens the 2D materials world. The 2D materials exhibit many extraordinary physical properties. For example, the recently reported superconductivity behaviors of 2D MoS 2 and Weyl semimetal properties of WTe 2 [1,2] bring new physics and phenomenon to the scientific community. Among the various kinds of 2D materials, graphene is very unique as it is a semimetal with a highly tunable Fermi level because the density states near the Dirac point are very low. [3] Graphene is a promising material for high performance elec- tronic and optoelectronic devices [4,5] based on its outstanding properties, including high intrinsic carrier mobility, [6] micro- scale ballistic transport, [7] abnormal quantum Hall effect, [8] 97.7% constant transmittance of visible light, [9] extraordinary thermal conductivity, [10] and high Young’s modulus. [11] In the recent years, various kinds of techniques have been employed to enhance the performance of graphene-based devices. Surface adsorption of foreign molecules, [12,13] electrical gating, [14–16] and magnetic effects, [17,18] have been widely used to tune the electrical properties of graphene. However, graphene itself cannot effectively convert light into electricity as the band gap of graphene is zero. [19] Therefore, graphene/semiconductor heterostructure is a good choice for the conversion of incident light into electricity. Because graphene is atomically thin, mean- while, semiconductor has a suitable band gap for the absorption of incident light. Besides, the graphene/semiconductor junc- tion is reasonably much thinner than the commercial silicon p-n junction solar cells. [20] Thus, various kinds of front surface design techniques can be used directly on the junction region. Localizing the incident electromagnetic field on the graphene surface will be an efficient way for solar energy Adv. Energy Mater. 2016, 1600822 www.MaterialsViews.com www.advenergymat.de