Fabrication of CuInSe 2 Solar Cells by the Evaporation of Binary Selenide Compounds
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Fabrication of CuInSe2 Solar Cells by the Evaporation of Binary Selenide Compounds Doo Youl Lee, Jae Ho Yun, Byung Tae Ahn, Kyung Hoon Yoon1, and Jinsoo Song1 Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Taejon 305-701, Korea 1 Renewable Energy Research Department, Korea Institute of Energy Research, Taejon 305-343, Korea ABSTRACT CuInSe2 films were prepared by the three-stage process using the evaporation of In2Se3, Cu2Se and Se. In the third stage, the depth of Cu-poor surface region was precisely adjusted by the control of the evaporation rate of In2Se3 and Se. The interface between Cu-poor surface region and stoichiometric CuInSe2 film was characterized using AES, microEDAX, and RBS. The 9.59% efficiency was achieved in the 0.16 cm2 area cell. The efficiency is the same level of the CIS cell prepared using the element coevaporation, opening up the application of binary compounds for highly efficient Cu(In,Ga)Se2 cells. INTRODUCTION CuInSe2(CIS)-based thin films with direct band gap and high absorption coefficient are one of the promising absorbing materials for heterojunction solar cells. Technical advances in polycrystalline thin film technology have demonstrated photovoltaic devices with measured efficiencies greater than 18%(total area)[1,2], employing the coevaporation of Cu, In, Ga, and Se elements through a three-stage process. However, evaporation of element sources requires high temperature for evaporation. Instead of element sources, selenide compounds such as Cu2Se and In2Se3 can be a candidate for evaporation sources. Selenide compounds have been employed for the preparation of CIS films because they can be easily evaporated at relatively low temperature[3,4]. But the fabrication of CIS cells using selenide sources hasn’t been quite successful. Park et al. reported a low efficiency by sequentially depositing In2Se3 and Cu2Se at room temperature in the form of amorphous state and annealing at high temperature[5]. This paper reports the systematic characterization of the CIS films and further improvement of cell efficiency of CIS cells up to 9.59% in the area of 0.16 cm2.
EXPERIMENT CIS films were prepared by the three-stage process using the evaporation of In2Se3, Cu2Se and Se. The 1737 Corning glass and soda-lime glass were used as substrates. The thicknesses of In2Se3 and Cu2Se layers were separately monitored using a quartz oscillator. In the first stage, In2Se3 and Se elements were evaporated on substrates at 150 oC to form In2Se3 layer with the thickness of 1 µm. In the second stage, Cu2Se was evaporated and reacted directly with the In2Se3 layer at 440 oC, so that Cu-rich CIS film was formed. The deposited CIS films were annealed at 440 oC for 10 min in a Se atmosphere in the same evaporation chamber. In the third stage, a small amount of In2Se3 and Se elements were evaporated to the CIS layer in order to eliminate the secondary Cu2-xSe phase and form a thin CuIn3Se5 layer[6]. H8.8.1
CIS cells with the structure of Ag/n-ZnO/i-ZnO/CdS/CuIn
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