Passivating electron-selective contacts for silicon solar cells based on an a-Si:H/TiOx stack and a low work function metal

Abstract

In this work, the ATOM (intrinsic a-Si:H/TiOx/low work function metal) structure is investigated to realize high-performance passivating electron-selective contacts for crystalline silicon solar cells. The absence of a highly doped Si region in this contact structure is meant to reduce the optoelectrical losses. We show that a low contact resistivity (rho(c)) can be obtained by the combined effect of a low work function metal, such as calcium (Phi 2.9eV), and Fermi-level depinning in the metal-insulator-semiconductor contact structure (where in our case TiOx acts as the insulator on the intrinsic a-Si:H passivating layer). TiOx grown by ALD is effective to achieve not only a low rho(c) but also good passivation properties. As an electron contact in silicon heterojunction solar cells, inserting interfacial TiOx at the i-a-Si:H/Ca interface significantly enhances the solar cell conversion efficiency. Consequently, the champion solar cell with the ATOM contact achieves a V-OC of 711 mV, FF of 72.9%, J(SC) of 35.1 mA/cm(2), and an efficiency of 18.2%. The achievement of a high V-OC and reasonable FF without the need for a highly doped Si layer serves as a valuable proof of concept for future developments on passivating electron-selective contacts using this structure.