Chromium Trioxide Hole-Selective Heterocontacts for Silicon Solar Cells

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 (CrOx, 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 CrOx 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 CrOx (2 nm)/Ag (30 nm)/CrOx (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 CrOx film and the depinning of the Fermi level of the SiOx layer at the silicon interface. Implementing the advanced hole-selective contacts with CrOx/Ag/CrOx 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 CrOx. Compared with the commercialized p-type solar cell, the novel CrOx-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.