Improving the efficiency of copper indium gallium (Di-)selenide (CIGS) solar cells through integration of a moth-eye textured resist with a refractive index similar to aluminum doped zinc oxide

Abstract

Textured transparent conductors are widely used in thin-film silicon solar cells. They lower the reflectivity at interfaces between different layers in the cell and/or cause an increase in the path length of photons in the Si absorber layer, which both result in an increase in the number of absorbed photons and, consequently, an increase in short-circuit current density (Jsc) and cell efficiency. Through optical simulations, we recently obtained strong indications that texturing of the transparent conductor in copper indium gallium (di-)selenide (CIGS) solar cells is also optically advantageous. Here, we experimentally demonstrate that the Jsc and efficiency of CIGS solar cells with an absorber layer thickness (dCIGS) of 0.85 μm, 1.00 μm and 2.00 μm increase through application of a moth-eye textured resist with a refractive index that is sufficiently similar to AZO (nresist = 1.792 vs. nAZO = 1.913 at 633 nm) to avoid large optical losses at the resist-AZO interface. On average, Jsc increases by 7.2%, which matches the average reduction in reflection of 7.0%. The average relative increase in efficiency is slightly lower (6.0%). No trend towards a larger relative increase in Jsc with decreasing dCIGS was observed. Ergo, the increase in Jsc can be fully explained by the reduction in reflection, and we did not observe any increase in Jsc based on an increased photon path length.

Optical study of back-contacted CIGS solar cells

“…This leads to 38.8 mA/cm 2 of J ph , which shows a significant improvement of 52.4% compared to the reference CIGS solar cell. Considering the fact that this value of J ph is much higher than that of a previously fabricated cell [4,8] with a more-than-three-times thicker absorber, this new structure is valuable for further research and therefore opening new ways towards highefficiency and cost-effective CIGS solar cells. An extensive electrical modelling is essential for optimizing also the electrical performance, which will be provided by authors by the time of the conference.…”

Optical Design of Textured Thin-Film CIGS Solar Cells with Nearly-Invisible Nanowire Assisted Front Contacts

“…Modeling is a good way to evaluate a wide array of parameters and to determine the impact of the design of devices and equipment on their functionality [ 30 , 35 ]. Optical modeling is powerful for gaining insight into what would otherwise be invisible or impossible to measure, especially in the nanosized domain [ 23 , 36 , 37 ].…”

“…Previously, our group has shown design optimization of micro-sized grids as well as nanotexturization of the TCO [ 4 , 7 , 29 ]. Moreover, the beneficial optical effect of a nanoimprinted anti-reflection coating was experimentally demonstrated on top of a CIGS cell [ 30 , 31 ].…”

Exploiting the Optical Limits of Thin‐Film Solar Cells: A Review on Light Management Strategies in Cu(In,Ga)Se2

“…[ 168 ] Burghoorn et al patterned a moth‐eye architecture with an average height and pitch of 350 and 300 nm, respectively, on a resist layer on top of thin‐film CIGS solar cell devices. [ 169 ] The developed texture enabled for ≈8% decrease of the device's average relative reflectance, which led to a 10.6% increase of the J sc over a flat reference device, for an absorber thickness of 1000 nm. [ 169 ] Furthermore, different CIGS layer thicknesses (2000, 1000, and 850 nm) were employed and no trend toward a larger relative J sc increase with decreasing CIGS thickness was observed.…”