Multiterminal structures for improved efficiency a-Si/μc-Si tandem devices

The main disadvantage of silicon thin-film technology is known to be its relatively low efficiency. By comparing not only the efficiency under standard test conditions but also the behavior under real outdoor conditions the following paper presents the high potential of four-terminal structure over standard two-terminal tandem module to substantially improve the yield in kWh/kW_p. Under standard test conditions the four-terminal module exhibits an initial efficiency of 11.7% compared to 10.6% for the state-of-the-art two-terminal tandem module. Under real outdoor conditions, the gain ranges from 10% for high irradiance to about 25% for low irradiance. These outdoors results have been confirmed by measurements conducted in Certisolis (French certification institute) as well as light soaking studies. Moreover the four-terminal modules consist in a combination of amorphous and microcrystalline modules deposited in industrial reactors, thus indicating the possibility to transfer rather easily this structure into production.