AGATHA · Advanced Gratting for Thin Films Solar Cell

The minority carrier diffusion lengths are small in polycrystalline or amorphous materials used in thin film solar cells, requiring thin layers to maximize charge collection. This is contradictory for the requirement to maximize solar energy absorption. The optical design consisting in increasing solar cell’s light-trapping capability is of prime importance. In order to provide total internal reflection, both randomly textured surfaces and regularly patterned surfaces have been investigated. No one of these approaches provides optimal light trapping because no one is suitable for the broad solar spectrum.Recent approaches involving new TCO layers show that double textures provide improved scattering. The AGATHA project aims to realize an advanced light trapping design by combining micro-texturing of glass by hot embossing and nano-texturing of the top TCO layer by etching. The parameters of this “modulated surface texture” can be adjusted to maximize the light scattering in all the solar spectrum to provide a significant increase in both short-circuit current and EQE. Suitable for high production throughput, the new texturation process chain developed in AGATHA fits with the intrinsic low cost nature of thin film solar cellsTo demonstrate the efficiency of this optical trapping design, the modulated texture concept will be implemented in a-Si:H based, µ-c-Si:H based and CIGS based thin films technologies. The objective is to reduce the active material thickness, from 250 nm up to 150 nm for the a-Si:H, from 1.5 µm up to 1 µm for µc-Si:H and from 2.5 µm up to 800 nm for the CIGS, when increasing the short circuit current of 15 % The choice of these technologies aims to maximize the impact by addressing 70% of the thin film market. According to typical solar cells cost structure, a 15 % reduction of the cost/m2 is achievable. Combined with the Jsc improvement, the implementation of modulated surface texture should result in a 20 % decrease of the €/W indicator.AGATHA is an EU coordinated project in the framework of call FP7-ENERGY-2010-INDIA, foreseeing a simultaneous start with the Indian coordinated project. Accordingly, the Indian project should start at the latest within 3 months of the signature of the EU grant agreement.