Production Technology of Large-Area, Light-Weight, Flexible Solar Cell and Module

Abstract

Production technologies of a-Si/a-SiGe flexible film solar cells have been established. The film solar cells having a unique monolithic device structure using through-hole contacts are continuously fabricated on flexible plastic films. Production technologies, such as (1) low temperature and high speed textured electrode deposition method, (2) high speed amorphous silicon deposition method, (3) modified roll-to-roll deposition apparatus technology, (4) large-area high quality transparent electrode deposition method, and (5) very high speed laser patterning method were developed. Increasing deposition rate of textured metal electrode was developed for improving production capacity. We developed and proposed low-temperature textured electrode deposition technique named “selective reactive sputtering”. In the deposition method, Ag-based electrode is deposited using small amount of Al containing Ag alloy targets. Ar/O2 mixed gas is used for reactive sputtering. In the deposition conditions, Ag is not oxidized and maintains low resistivity, whereas Al is oxidized selectively and changes the surface morphology drastically. The oxide incorporation affects on the surface reaction and enhances surface roughness formation. We also developed an amorphous silicon deposition control method which can increase deposition rate without deteriorating film properties. We found peak-to-peak voltage at the cathode (Vpp) had information of the plasma and could be used for optimizing the deposition conditions. Vpp has a strong relationship with stabilized efficiency of solar cells. Very high laser patterning method was also developed. The laser patterning method using a galvano scanner improves the pattering speed remarkably. Our new factory in Kumamoto started commercial production in the last year. We can produce 12MW/Y of solar cells using the new production line that can apply 1m-wide and 2000m-long film substrates at this time. We are planning to install more production lines and have 40MW/Y production capacity in FY 2008.