SnO2/Mg combination electron selective transport layer for Si heterojunction solar cells

In this paper, SnO2 prepared by sol-gel method was spin-coated on textured n-type crystalline silicon (c-Si) wafers to replace phosphorus doped n-type hydrogenated amorphous silicon (a-Si:H) in novel Si heterojunction (SHJ) solar cells. Good coverage of the sol-gel SnO2 layer on pyramidal textured silicon substrate was achieved. It was demonstrated that a low-work-function metal electrode is necessary for the dopant-free electron transport layer. The SnO2/Mg combination layer was determined to have a low-work-function feature and exhibit a synergistic effect in promoting the selective transport of carriers. A combination passivation layer containing intrinsic amorphous silicon (a-Si:H(i)) and SiOx which was formed from UV-O3 photo oxidation of the a-Si:H(i) surface for a short time was used to passivate the interface between the SnO2 and the c-Si. The new type a-Si:H/SiOx/SnO2/Mg contact is effective to achieve not only a low contact resistivity but also good passivation properties. Finally, a power conversion efficiency (PCE) of 18.6% and an open circuit voltage of 695 mV was achieved on a novel SHJ solar cell with an a-Si:H(i)/SiOx combination passivation layer and a SnO2/Mg combination electron selective transport layer.