Low‐Temperature N 2 Annealing Enabling Front Junction MoO x /Si Heterojunction Solar Cell With Screen‐Printed Metal Grids

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ABSTRACT Transition metal oxides (TMOs) such as MoO x , featuring a high work function and a wide optical bandgap, are competitive alternatives to p‐type a‐Si:H or nano crystalline silicon in silicon heterojunction solar cells to form silicon compound heterojunction (SCH) solar cells. However, the thermal instability of MoO x during the curing process of screen‐printing restrains its massive production in industry. In this work, silver grids are printed on the MoO x side of MoO x SCH solar cells, and the influence of annealing atmosphere and temperature on the performance of the solar cells is investigated. After annealing in O 2 or air, the device performance is significantly degraded, while it remains almost unchanged after annealing in N 2 at 136°C. A conversion efficiency of 22.40% is achieved on the SCH solar cells with screen‐printed Ag grids when annealed at 136°C for 40 min in N 2 atmosphere, which is equivalent to that of the solar cells with thermally evaporated grids. To reveal the annealing effect, systematic research is conducted on changes in optoelectronic property, contact resistivity, and compositional distribution of MoO x , brought about by annealing in N 2 , O 2 , and air at different temperatures. Oxygen vacancies and conductivity both increase after annealing in N 2 , contributing to more efficient hole carrier collection through defect state‐assisted band‐to‐band transition. However, dipoles formed at the c‐Si/MoO x interface during N 2 annealing, proposed according to the calculation of differential charge density, might hinder the hole transportation from c‐Si to MoO x . A 1‐nm Al 2 O 3 layer inserted between a‐Si:H(i) and MoO x is found to be effective for mitigating the V oc drop after annealing in air. The approaches exhibit great potential for implementing screen‐printing on MoO x SCH solar cells, rendering industrial production of MoO x SCH solar cells feasible.

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