High-efficiency, point-contact silicon solar cells for Fresnel lens concentrator modules

Point-contact silicon solar cells have been developed for Fresnel lens concentrator modules. The cells have an area of 1.21 cm² on a 12×12 mm die. The design incident flux on the cell is 22.3 W/cm². A new cell design and process have been developed to insure a high efficiency and a large fabrication yield, and to eliminate hazardous materials and pyrophoric gases. The new process is very safe and benign to the environment. Also, a new passivation technique for the front surface has been discovered which makes the point-contact cell fully stable under steady-state concentrated sunlight. No degradation has been observed so far after more than 200 days of exposure behind Fresnel lenses providing an incident power density of 36 W/cm². An improved anti-reflection coating and an improved light trapping, giving an average effective number of passes of the infra-red light greater than 25, are part of the developments. The best cell shows an efficiency of 26% under 100 suns (AM1.5D, 25°C). The typical cell efficiency is greater than 25% at 200 suns. The cells are easily solderable due to a double-level metallization and three large copper pads. The cells are now produced in large quantities in a pilot line located in a Class 100 clean room which has a capacity of 7.5 MW per year of concentrator solar cells