Interface passivation by Al2O3 and SnO2 at the CdTe solar cell front contact

doi:10.3969/j.issn.0253-2778.2020.04.009

Abstract

Abstract: Al2O3 and SnO2 thin layers employed as the passivation layer for MgxZn1-xO(MZO)/CdTe thin-film solar cells were grown by RF magnetron sputtering. Time-resolved photoluminescence (TRPL)spectroscopy spectra show that the minority carrier lifetime of the MZO/Al2O3/CdTe structure is much longer than that of the MZO/CdTe structure, indicating that Al2O3 has a strong passivation effect on CdTe. However, the CdTe solar cells with Al2O3 as the passivation layer demonstrate serious “S-kink” in the light current density-voltage curves. The band alignment of solar cells with different passivation layer were analyzed by X-ray photoelectron spectroscopy (XPS). The large conduction band offset between Al2O3 and CdTe was found to be responsible for the “S-kink” for the solar cells with Al2O3. By controlling the thickness of the SnO2 layer, quantum size effect can be used to adjust the conduction band offset between SnO2 and CdTe, thus reducing the “S-kink” phenomenon, improving the filling factor and short-circuit current density. A solar cell with an efficiency of 9.7% has been fabricated. This study demonstrates that large conduction band offset is the main reason for the “S-kink” in the J-V curves, and that reducing the conduction band offset can effectively decrease the “S-kink” phenomenon and increase the solar cell efficiency.

Key words: CdTe, thin film solar cells, passivation, band alignment

CLC Number:

TM914.42

ZHENG Genhua, WANG Dongming, WU Lingling, WANG Guangwei, CAI Yanbo, WANG Deliang. Interface passivation by Al2O3 and SnO2 at the CdTe solar cell front contact[J]. Journal of University of Science and Technology of China, 2020, 50(4): 450-456.

References

［1］ GREEN M A, HISHIKAWA Y, DUNLOP E D, et al. Solar cell efficiency tables (version 52)[J]. Progress in Photovoltaics: Research and Applications, 2018, 26(7): 427-436.
[2] MUNSHI A H, KEPHART J, ABBAS A, et al. Polycrystalline CdSeTe/CdTe absorber cells with 28 mA/cm2 short-circuit current[J]. IEEE Journal of Photovoltaics, 2017, 8(1): 310-314.
[3] METZGER W K, GROVER S, LU D, et al. Exceeding 20% efficiency with in situ group V doping in polycrystalline CdTe solar cells[J]. Nature Energy, 2019, 4(10): 837-845.
[4] ZHENG X, KUCIAUSKAS D, MOSELEY J, et al. Recombination and bandgap engineering in CdSeTe/CdTe solar cells[J]. APL Materials, 2019, 7(7): 071112.
[5] KEPHART J M, MCCAMY J W, MA Z, et al. Band alignment of front contact layers for high-efficiency CdTe solar cells[J]. Solar Energy Materials and Solar Cells, 2016, 157: 266-275.
[6] ABLEKIM T, PERKINS C, ZHENG X, et al. Tailoring MgZnO/CdSeTe interfaces for photovoltaics[J]. IEEE Journal of Photovoltaics, 2019, 9(3): 888-892.
[7] DELAHOY A E, PENG S, PATRA P, et al. Cadmium tin oxide and zinc magnesium oxide prepared by hollow cathode sputtering for CdTe photovoltaics[J]. MRS Advances, 2017, 2(53): 3203-3214.
[8] LI D B, SONG Z, AWNI R A, et al. Eliminating S-kink to maximize the performance of MgZnO/CdTe solar cells[J]. ACS Applied Energy Materials, 2019, 2(4): 2896-2903.
[9] KEPHART J M, KINDVALL A, WILLIAMS D, et al. Sputter-deposited oxides for interface passivation of CdTe photovoltaics[J]. IEEE Journal of Photovol-taics, 2018, 8(2): 587-593.
[10] NOWICKI R S. Properties of rf-sputtered Al2O3 films deposited by planar magnetron[J]. Journal of Vacuum Science and Technology, 1977, 14(1): 127-133.
[11] CHOW S. Engineering the fixed charge of aluminum oxide for field-assisted passivation in heterojunction solar cells[C]// 2015 NNIN REU Research Accomplishments. Ithaca, NY: National Nanotechnology Infrastructure Network, 2015: 168-169.
[12] BANSAL A, SRIVASTAVA P, SINGH B R. On the surface passivation of c-silicon by RF sputtered Al2O3 for solar cell application[J]. Journal of Materials Science: Materials in Electronics, 2015, 26(2): 639-645.
[13] BAKBAK B, GEDIK S, KOKTEKIR B E, et al. Structural and functional assessment in patients treated with systemic isotretinoin using optical coherence tomography and frequency-doubling technology perimetry[J]. Neuroophthalmology, 2013, 37(3): 100-103.
[14] SIMON D K, JORDAN P M, MIKOLAJICK T, et al. On the control of the fixed charge densities in Al2O3-based silicon surface passivation schemes[J]. ACS applied Materials & Interfaces, 2015, 7(51): 28215-28222.
[15] PUDOV A O, SITES J R, CONTRERAS M A, et al. CIGS J-V distortion in the absence of blue photons[J]. Thin Solid Films, 2005, 480: 273-278.
[16] WANG T, REN S, LI C, et al. Exploring window buffer layer technology to enhance CdTe solar cell performance[J]. Solar Energy, 2018, 164: 180-186.
[17] LI X, SHEN K, LI Q, et al. Roll-over behavior in current-voltage curve introduced by an energy barrier at the front contact in thin film CdTe solar cell[J]. Solar Energy, 2018, 165: 27-34.
[18] SHEN K, LI Q, WANG D, et al. CdTe solar cell performance under low-intensity light irradiance[J]. Solar Energy Materials and Solar Cells, 2016, 144: 472-480.
[19] WANG M, LI X, WANG D. Ultrathin CdTe solar cells with absorber layer thinner than 0.2 microns[J]. The European Physical Journal Applied Physics, 2018, 83(2): 20101.
[20] XIAO D, LI X, WANG D, et al. CdTe thin film solar cell with NiO as a back contact buffer layer[J]. Solar Energy Materials and Solar Cells, 2017, 169: 61-67.
[21] SHEN K, YANG R, WANG D, et al. Stable CdTe solar cell with V2O5 as a back contact buffer layer[J]. Solar Energy Materials and Solar Cells, 2016, 144: 500-508.
[22] XU X, ZHUANG J, WANG X. SnO2 quantum dots and quantum wires: controllable synthesis, self-assembled 2D architectures, and gas-sensing properties[J]. Journal of the American Chemical Society, 2008, 130(37): 12527-12535.
[23] SONG T, KANEVCE A, SITES J R. Emitter/absorber interface of CdTe solar cells[J]. Journal of Applied Physics, 2016, 119(23): 233104.

()
()