Laser assisted formation of locally defined Cu(In,Ga)Se₂ microstructures

In this work, the local nucleation of Cu(In,Ga)Se₂ absorbers at micrometer scale is investigated. The aim is to reduce the consumption of indium and gallium for micro-concentrator Cu(In,Ga)Se₂ solar cells.

Our results show that the selective formation of In and Ga islands on molybdenum-coated soda-lime glass-substrates is possible by using an optical system integrated into a metal organic chemical vapor deposition (MOCVD) chamber. For this purpose, an infrared laser is integrated with a diffractive optical element (DOE). The DOE diffracts the incident beam into a matrix of 7*7 output beams. The output beams which are directed to the substrate are absorbed in the molybdenum and heat it locally.

At the same time, the metal organic precursor gases trimethylindium and triethylgallium diluted by the carrier gas (here N₂) are introduced into the chamber. The local heating of the substrate decomposes the precursor and leads to the growth of metal islands (here indium and gallium). As a result, the nucleation of In and Ga islands can be locally controlled by this sophisticated heating setup. Subsequent evaporation of copper in a PVD-chamber followed by selenization leads to the formation of Cu(In,Ga)Se₂ islands that can serve as micro-absorbers. Since the size and pattern of the formed Cu(In,Ga)Se₂ islands can be easily controlled using this laser-heating/DOE-setup, this novel method can also be applied to large-scale production.