Solar cells???

Researchers at the the Fraunhofer Institute for Solar Energy Systems have improved the efficiency of crystalline silicon-based solar cells.

The solar cells themselves have a thickness of 37 micrometres and an efficiency of 20.2 %. In comparison, current industrial cells are comparatively thick – 300 micrometers – and are significantly less efficient at 16%.

“The enormous potential that is still offered by the well-proven crystalline silicon technology is immediately obvious”, according to Gerhard Willeke, Head of the Solar Cell Department, “and we now have the technology to realise this potential in industrial production”.

The researchers in Freiburg have developed an inexpensive process that allows these highly efficient solar cells to be produced from thin silicon wafers.

LFC technology (laser fired contacts) is then used to make a contact on the back surface of the solar cell, replacing the slow and expensive photolithographic processing steps which are in use today.

“In LFC processing, we evaporate an aluminium layer directly onto a passivation layer and then fire through the metal with a laser to create the local contacts”, explained Stefan Glunz, the co-ordinator of work at the Institute on monocrystalline silicon solar cells.

This process is inexpensive, requires only one second per solar cell, does not impose significant stress on the material, and functions for all wafer thicknesses and doping levels, making it ideal for industrial mass production.

A niche market for extremely thin, high-efficiency cells already exists in aeronautic and space applications. However, to make the cells attractive for terrestrial applications, an appreciable amount of research and development is still needed to manufacture the extremely thin wafers economically.

The development of solar cells from extremely thin wafers is being investigated within a project funded by the German Federal Ministry for the Environment, Nature Conservation and Reactor Safety (BMU).