Analysis of quantum efficiency and optical enhancement in amorphous Si p–i–n solar cells

Abstract

The effect of i‐layer thickness, tin oxide texture, and back reflector (BR) on optical enhancement has been systematically studied in a series of 20 a‐Si p–i–n solar cells. The internal quantum efficiency has been analyzed by a simple model based on the work of Schade and Smith. The enhancement of optical absorption is characterized by m, a wavelength‐dependent fitting parameter representing the increase in optical pathlength relative to the i‐layer thickness d. Solar cells with an Al BR have negligible optical enhancement, with m < 1.5, consistent with large parasitic absorption at the Al/Si interface as reported by others. Solar cells on highly textured SnO2 with ZnO/Al or ZnO/Ag BR have peak values of m ∼ 3–4, with ZnO/Ag having slightly larger values than ZnO/Al. It was found that m has a strong dependence on the product αd, and that maximum values of m increase with reflectivity of the BR. It is shown that a major source of parasitic absorption loss at long wavelengths is light trapping in the textured SnO2 front contact. Copyright © 2002 John Wiley & Sons, Ltd.

Hybrid Dielectric-Metallic Back Reflector for Amorphous Silicon Solar Cells

“…In addition, the distance between the absorption curves, becomes remarkably small after the 500 nm thickness. Also, the 500 nm thickness, is in line with other optical studies performed on a-Si solar cells [12,25,37].…”

“…The optical structure presented in this paper is transferable to some of the a-Si solar cell configurations that have been reported, such as the one presented in [12]. More detailed accounts that specifically address TCO applications in a-Si solar cells can be found in the following references [12][13][14][15][16].…”

“…However, the science of back surface reflectance is dictated by a number of important aspects, in addition to the reflective properties. These aspects include the back contact technology, material conductivity, passivation and the material adherence properties [12,16]. The combination of these features gives rise to a complex interplay, between the optical and electrical functionality.…”

“…On inspection of the absorption coefficient data for a-Si, it is evident that most of the incident light energy is absorbed within the first three hundred nanometers of an a-Si structure [16]. However, many of the papers on a-Si solar cells, have the active layer thicknesses ranging from a few hundred nanometers to a number of microns [12][13][14]25,36]. With there being such great variation in the choice of active layer thicknesses, we decided to perform a fundamental analysis on the absorption characteristics of a-Si structures, as is shown in Figure 2a.…”

Improving solar cell efficiency with optically optimised TCO layers

“…We will show though, that one technology relevant to our discussion, that has gained a more widespread use -the roughening the TCO surface -can be equivalent to an anti-reflective layer in the low haze regime. Even a small roughness does lead to a reduction in the TCO/absorber reflective losses in addition to the more often discussed changes in the light path for a large roughness, enhancing the absorption in the active layer [7][8][9][10].…”