Status of high efficiency, low cost n-type silicon solar cells

In this article we report on the latest update of our double-side contacted n-type Cz Si based back junction solar cell development. The solar cells have been manufactured by adopting a new low cost emitter formation process instead of a high-temperature boron diffusion tube furnace process. This approach allows for the reduction of the process complexity and therefore costs which are driven to a level similar to those of a standard p-type Si PERC process. The impact of the rear contact design of the n-Si solar cell is studied by using line and point contacts and various metal fractions of the point contact (7 % to 29 %). The n-Si solar cell structure with line contacts (fraction of 7 %) resulted in an efficiency of 19.2 % with an open circuit voltage of 647 mV and a fill factor of 74.2 %. The use of a point contact pattern (fraction of 7 %) improved the efficiency to 21.3 % with an open circuit voltage of 663 mV and a fill factor of 79.1 %. The gain of the open circuit voltage results in an efficiency gain of 0.5 %abs. The main efficiency gain of 1.2 %abs is related to an improvement of the fill factor which can be mainly attributed to a reduction of the series resistance losses. After exposing the solar cells to 25 °C and 75 °C at 1 sun illumination for 24 hours no degradation of the performance is observed which proofs the expected stability of n-type Cz Si based solar cells.