Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014)
    Energy Harvesting & Storage Tuesday Sessions
       Session EH-TuP

Paper EH-TuP14
Feasibility Study on Graphene as Back Contact for Cu(InGa)Se2 Thin Film Solar Cells

Tuesday, December 9, 2014, 4:00 pm, Room Mauka

Session: Energy Harvesting & Storage Poster Session
Presenter: Hee-San Ryu, Yeungnam University, Republic of Korea
Authors: H.-S. Ryu, Yeungnam University, Republic of Korea
K. Moon, Yeungnam University, Republic of Korea
Y. Jun, Korea University, Republic of Korea
J. Kim, Korea University, Republic of Korea
W.K. Kim, Yeungnam University, Republic of Korea
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Chalcopyrite Cu(InGa)Se2 (CIGS) solar cells have been considered as the most promising thin film solar cell, holding a record cell efficiency of 20.9% (Solar Frontier, 2014), which is slightly higher than that of multi-crystalline Si solar cells (20.4%). Molybdenum (Mo) is the most common material used as a back contact electrode for CIGS solar cells due to its low cost and electrical suitability with CIGS layer. In this paper, mono- or multi-layer graphene has been explored as an alternative back contact electrode to replace Mo layer. As a back contact electrode, graphene has many attractive properties such as high flexibility, excellent optical transmittance, low resistance, and high mechanical and chemical stabilities. In particular, transparent back contact like a graphene is essential to bifacial photovoltaic cells that can absorb lights from the front and back sides. In this study, the graphene films produced by chemical vapor deposition process on Cu foil were transferred onto soda-lime glass substrate using a simple wet-based transfer process. Graphene-coated glass was analyzed by tape test, four point probe measurement and UV visible spectroscopy to evaluate adhesion strength, resistance and transparency, respectively. CIGS absorbers were then deposited onto graphene-coated glass by using 3-stage co-evaporation process in a vacuum evaporator. A series of characterizations including X-ray diffraction, scanning electron microscopy and raman spectroscopy were performed to investigate the effect of number of graphene layers (e.g., 1, 2 and 4 layers) on the formation of chalcopyrite CIGS structure, and compare the characteristics of CIGS absorbers on different back contacts, graphene vs. Mo layers.