Enhancement of the photocurrent and efficiency of CdTe solar cells suppressing the front contact reflection using a highly-resistive ZnO buffer layer

• Published in: Solar energy materials and solar cells Vol. 191; pp. 78 - 82
• Main Authors: Kartopu, G., Williams, B.L., Zardetto, V., Gürlek, A.K., Clayton, A.J., Jones, S., Kessels, W.M.M., Creatore, M., Irvine, S.J.C.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.03.2019; Elsevier BV
• Subjects: ALD; Anti-reflection; Buffer layers; Cadmium tellurides; CdTe; Chemical vapor deposition; Efficiency; Energy conversion efficiency; Film thickness; Light effects; MOCVD; Organic chemistry; Photoelectric effect; Photoelectric emission; Photovoltaic cells; Photovoltaic conversion; Photovoltaics; Reflectance; Reflection; Solar cells; Spectral sensitivity; Thin film PV; Zinc oxide; ZnO; ALD; ZnO; CdTe; MOCVD; Thin film PV; Anti-reflection
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2018.11.002

We report on the effects of using an atomic layer deposited ZnO transparent buffer layer with > 106 Ω cm resistivity on the performance of CdZnS/CdTe solar cells grown by metalorganic chemical vapour deposition (MOCVD). The buffer film thickness is adjusted by optical modelling to suppress the reflection losses at the front contact. A clear improvement, up to 1.8% in conversion efficiency, was obtained in comparison to reference devices without the ZnO buffer layer, thanks to the enhancement of the current density (Jsc) and fill factor (FF). Device spectral response showed improved collection for most of the visible region. Reflectance measurements confirmed that the ZnO film reduced the optical reflectance around the transparent front contact. This effect permitted light management through the front contact leading to an improvement of the Jsc and hence the photovoltaic conversion efficiency. These results are intriguing since the literature on CdTe solar cells did not previously report improvement to the photocurrent and device response through controlling the highly-resistive transparent buffer layer. The light J-V curves (left) and EQE spectrum (right) of CdTe solar cells with and without a ZnO HRT layer. PV enhancement of CdTe thin film solar cells using a 50 nm ALD ZnO buffer film reported. Reduced reflection at the front contact region contributed to the photocurrent significantly, boosting the conversion efficiency up to 1.8%. Optical engineering of the transparent front contact may further improve anti-reflection property and PV performance of CdTe thin film solar cells. [Display omitted] •ALD grown ZnO films used in CdTe thin film solar cells as highly-resistive-transparent (HRT) buffer to impart AR effect.•BBoth the Jsc and FF improved significantly•Jsc gain originates mainly from reduced reflection at the front contact as predicted by the optical model.•Up to 1.8% net gain in conversion efficiency obtained using the ZnO HRT layer.