Bifacial 8.3%/5.4% front/rear efficiency ZnO:Al/n-Si heterojunction solar cell produced by spray pyrolysis

Abstract

Using an as-deposited Al-doped ZnO (AZO) film synthesized by ultrasonic spray pyrolysis directly onto crystalline silicon (c-Si), we demonstrate a bifacial AZO/n-Si heterojunction solar cell (HJSC) with high efficiency of 8.3%/5.4% under front/rear illumination. To optimize fabrication process, the influence of substrate temperature TD (in the range 310–460°C), annealing, and film thickness d on the film and AZO/c-Si junction properties were studied systematically. SEM, ellipsometry, EDX spectroscopy, transmission, reflection, and external quantum efficiency spectra, resistivity ρ, Hall, Suns–Voc, and light I–V measurements were used for the analysis. Annealed junctions, AZO/n-Si and AZO/p-Si, as well as AZO/p-Si junction with as-deposited films showed small open-circuit voltage Voc (<300mV). The highest Voc (∼480mV) showed AZO/n-Si junction with as-deposited film grown at 410°C. We employed as-deposited AZO films grown at 410°C in AZO/(nn+)Cz-Si/In2O3:F bifacial heterojunction solar cells, which differed only in the AZO film thickness. Increasing d from 260 to 910nm resulted in the following: (1) the photocurrent did not changed; (2) ρ and Rsh of the film, Voc and the series resistance of the HJSCs decreased; (3) the fill factor FF and efficiency η increased (for front illumination, FF: from 29.1 to 57.3%, η: from 3.3 to 8.3%, respectively). At rear illumination, the best cell showed the efficiency of 5.4%. At 1-sun front illumination and 20–50–100% 1-sun rear illumination, such a cell will generate energy approaching that produced by a monofacial solar cell of 9.1–10.3–12.1% efficiency.