Chromium Trioxide Hole-Selective Heterocontacts for Silicon Solar Cells

Abstract

A high recombination rate and high thermal budget for aluminum (Al) back surface field are found in the industrial p-type silicon solar cells. Direct metallization on lightly doped p-type silicon, however, exhibits a large Schottky barrier for the holes on the silicon surface because of Fermi-level pinning effect. As a result, low-temperature-deposited, dopant-free chromium trioxide (CrO _x, x < 3) with high stability and high performance is first applied in a p-type silicon solar cell as a hole-selective contact at the rear surface. By using 4 nm CrO _x between the p-type silicon and Ag, we achieve a reduction of the contact resistivity for the contact of Ag directly on p-type silicon. For further improvement, we utilize a CrO _x (2 nm)/Ag (30 nm)/CrO _x (2 nm) multilayer film on the contact between Ag and p-type crystalline silicon (c-Si) to achieve a lower contact resistance (40 mΩ·cm²). The low-resistivity Ohmic contact is attributed to the high work function of the uniform CrO _x film and the depinning of the Fermi level of the SiO _x layer at the silicon interface. Implementing the advanced hole-selective contacts with CrO _x/Ag/CrO _x on the p-type silicon solar cell results in a power conversion efficiency of 20.3%, which is 0.1% higher than that of the cell utilizing 4 nm CrO _x. Compared with the commercialized p-type solar cell, the novel CrO _x-based hole-selective transport material opens up a new possibility for c-Si solar cells using high-efficiency, low-temperature, and dopant-free deposition techniques.