Post-annealing effect on the reactively sputter-grown CIGS thin films and its influence to solar cell performance |
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Institution: | 1. Cheongju University, 298 Daesung-ro, Sangdang-gu, Cheongju, Chungbuk 360-764, Republic of Korea;2. Electronics and Telecommunications Research Institute, 218 Gajeongno, Yuseong-gu, Daejeon 305-700, Republic of Korea |
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Abstract: | Using a reactive co-sputtering from Cu0.6Ga0.4 and Cu0.4In0.6 alloy targets, we prepared CuIn1?xGaxSe2 (CIGS) thin films on Mo/soda-lime glass (SLG) in association with a thermal cracker for elemental atomic Se radicals. The film growth was performed at 500 °C for 90 min. To achieve the composition ratio of CIGS absorber layer, Cu0.6Ga0.4 target was set at RF power of 50 W, 60 W, 70 W, and 80 W while keeping at 100 W for Cu0.4In0.6 alloy target. Post-annealing was done for all the CIGS films at 550 °C for 30 min. The composition ratio of Cu]/In + Ga] and Ga]/In + Ga] was increased with RF power but showed no change after post-annealing. X-ray diffraction analysis revealed all the samples has grown dominantly in the 112] crystal orientation. We found the Cu2?xSe and (InGa)2?xSe3 defect phase both at the surface and in the bulk, and developed with post-annealing. From the devices fabricated in the structure of grid/ITO/i-ZnO/CdS/CIGS/Mo/soda-lime glass (SLG), the external quantum efficiency (EQE) was observed to improve in the wavelength, λ ≥ 550 nm in the samples treated with annealing. In the current–voltage (J–V) measurements, the solar cell showed the best performance of FF = 54.1%, Voc = 0.48 V, Jsc = 33.1 mA/cm2 and η = 8.5% in the sample with Cu]/In + Ga] = 0.84 that improved largely from η = 4.6% for the solar cell with an as-grown CIGS films. |
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Keywords: | Reactive co-sputtering CIGS Composition ratio Solar cell Post-annealing External quantum efficiency |
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