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Tham khảo tài liệu 'solar cells thin film technologies part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Development of Flexible Cu In Ga Se2 Thin Film Solar Cell by Lift-Off Process 409 Fig. 2. Photograph of flexible CIGS solar cells using PI film. Fig. 3. Photo J-V curves of flexible solar cells using PTFE red and PI blue films. Photo J-V curve of standard solar cell without lift-off process brack is also shown for comparison. Sample structure Eff Jsc mA cm2 Voc V FF PI flexible 5.9 25.7 0.420 54.9 PTFE flexible 6.6 25.6 0.445 57.9 Standard 11.4 36.9 0.497 62.4 Table 2. Solar cell parameters obtaind from flexible solar cells using PI and PTFE films. Solar cell parameters of standard solar cell are also shown for comparison. 410 Solar Cells - Thin-Film Technologies conversion efficiency Eff. and the fill factor FF are summarized in Table 2. The conversion efficiencies of the flexible solar cells are an approximately half conversion efficiency of the standard solar cell. EQE spectra of these solar cells are shown in Fig. 4. EQEs of the flexible solar cells remarkably decrease in the long wavelength region from 700 to 1200 nm compared to the standard solar cell. We discuss this cause as below. Fig. 4. EQE spectra of flexible solar cells using PTFE red and PI films blue . EQE spectrum of standard solar cell without lift-off process black is also shown for comparison. EQE spectra of flexible solar cells are similar irrespective of substrate materials. As shown in Fig. 5 a the band gap profile of the standard solar cell consists of the graded band gap structure because of the three-stage deposition process. The diffusion length of electrons generated by the long wavelength light near the back electrode is improved due to the quasi-electric field in which the CIGS layer forms Contreras et al. 1994b . The graded band gap structure is therefore beneficial for collecting the photogenerated carriers. On the other hand as shown in Fig. 5 b the band gap profile of the CIGS layer is inverted due to Photogenerated electron Surface Conduction band Rear surface Valence .
