Ni2P-a promising candidate for back contacts to CdS/CdTe solar cells

An important device issue that must be addressed for the use of CdTe solar cells in terrestrial applications is the formation of an effective and reliable back contact. Most successful efforts to date have been relying on the use of copper either in elemental form or in conjunction with other materials. Two examples are copper doped zinc telluride and copper telluride. Such efforts have yielded CdTe solar cells with state-of-the-art fill factors (>75%). However, the long-term stability of copper-based contacts is believed to play a major role in the observed performance degradation of CdTe/CdS solar cells. Nickel phosphide (Ni₂P) has been considered as an alternative back contact material. Nickel phosphide in powder form was mixed with a graphite paste and subsequently applied to CdTe for the formation of the back contact. Cadmium telluride solar cells were fabricated using this type of contact and the effect of various processing parameters such as annealing temperature, duration of annealing, and Ni₂P concentration have been studied. The best devices exhibited V_oc s in the range of 820-840 mV and FFs greater than 70% indicating that Ni₂P is a very promising candidate as a back contact material for CdTe solar cells