Current distribution unevenness incurred uncertain contact resistivity of silicon heterojunction solar cells

Abstract

In crystalline silicon (c-Si) solar cells, achieving high efficiency requires high-quality passivation and carrier extraction at the metallization interface. The classical transfer length method (TLM) is commonly used to characterize the contact resistivity (ρ_c) of c-Si solar cells. However, when extracting the ρ_c of high-efficiency solar cells via the TLM method, the accuracy of the measurements is challenging due to the large variety of multiple tests, especially for silicon heterojunction (SHJ) solar cells. Moreover, a crowding effect at the metal and silicon interface incurs the possibility of an unreliable ρ_c value in TLM measurement due to inhomogeneous current transport within the device, which impacts the uncertainty of the ρ_c extraction. We unveiled the impact factors on measuring the ρ_c between the silver (Ag) electrode and indium tin oxide (ITO) through experimental and simulation approaches in SHJ solar cells. The factors, including the probe numbers, contact positions, and the ITO sheet resistance, have been systematically investigated. Additionally, the related current density distributions under bias at different cross-sections within the ITO layer were explored through COMSOL simulations, providing a more intuitive explanation for the varieties of the measured contact resistance. This work offers insights into more precise ρ_c measurements and favors high-performance metallization of SHJ solar cells.