The use of copper in solar cells and modules

The most expensive non-silicon component of solar cells remain silver used for front contact. We propose a single step deposition of Cu/Ni metallization by screen printing method. It was achieved by coating the copper powder with a barrier layer mainly consisting of nickel, in a simple electroless process and then mixing it with a commercial silver paste at 30 wt%. Produced solar cells were fired at high temperature (940°C), which so far was unattainable due to the high diffusion coefficient of copper in elevated temperatures. Manufactured solar cells with an active area 243 cm2 were soldered into 4-solar cells mini module and laminated. Subsequently, the module was subjected to a thermal cycling test for 400 cycles. No signs of module delamination or visual degradation were observed. The I-V measurement results indicate that the power drop of the module is 3.3%, which meets the IEC 61215 standard requirements and confirms that nickel is an effective barrier and prevents copper diffusion into space charge region. For the reference sample with silver front metallization the power decrease was 1.5%. No significant difference in electrical parameters of test modules proves that the proposed copper-silver metallization is comparably stable as standard silver electrode.