Surface Passivation and Antireflection Behavior of ALD on n-Type Silicon for Solar Cells

Abstract

Atomic layer deposition, a method of excellent step coverage and conformal deposition, was used to deposit TiO2thin films for the surface passivation and antireflection coating of silicon solar cells. TiO2thin films deposited at different temperatures (200°C, 300°C, 400°C, and 500°C) on FZ n-type silicon wafers are in the thickness of 66.4 nm ± 1.1 nm and in the form of self-limiting growth. For the properties of surface passivation, Si surface is effectively passivated by the 200°C deposition TiO2thin film. Its effective minority carrier lifetime, measured by the photoconductance decay method, is improved 133% at the injection level of cm−3. Depending on different deposition parameters and annealing processes, we can control the crystallinity of TiO2and find low-temperature TiO2phase (anatase) better passivation performance than the high-temperature one (rutile), which is consistent with the results of work function measured by Kelvin probe. In addition, TiO2thin films on polished Si wafer serve as good ARC layers with refractive index between 2.13 and 2.44 at 632.8 nm. Weighted average reflectance at AM1.5G reduces more than half after the deposition of TiO2. Finally, surface passivation and antireflection properties of TiO2are stable after the cofire process of conventional crystalline Si solar cells.