Replicated microstructures with optical functions in solar and display applications

Abstract

By surface-relief structures optical functions like anti-reflection, light trapping or light distribution and re-direction can be realized. New applications in solar energy systems and in displays require structures with sub-micron features which are homogeneously distributed over large areas. This paper addresses the design and the whole experimental process chain from the micro structure origination on large areas to the replication and the system integration in the specific application. Topics are antireflective surfaces for solar systems and displays, light trapping in polymer solar cells, sun protection systems for facades and diffusers for projection displays and in glazing. For the micro structure origination we investigated the suitability of holographic recording in photoresist by using a large scale interferometer. An argon ion laser was used as a coherent light source at a wavelength of 364nm. With the interferometer set-up periodic and stochastic interference patterns were recorded in positive photoresist. In the case of periodic structures, grating periods between 200nm and 20µm have been realized. By carefully modeling resulting resist profiles it was possible to originate even prismatic surface-relief profiles. Structures with good homogeneity were originated on areas of up to 4800 cm² by optimizing the interferometer set-up and the photoresist processing.