Measurement of poly-Si film thickness on textured surfaces by X-ray diffraction in poly-Si/SiOx passivating contacts for monocrystalline Si solar cells

Polycrystalline Silicon on tunneling silicon oxide (poly-Si/SiOx) passivating contacts have shown great potential for the next-generation monocrystalline Si (c-Si) industrial photovoltaic technology. However, these cells typically suffer from strong parasitic absorption in the thick front poly-Si layer, which is designed to reduce metal-induced recombination. In previous work, we demonstrated an improved short-circuit current density, Jsc, by thinning the front poly-Si film in an SF6 plasma using the front metal grids as a self-aligned mask, but the sub – 100 nm thick poly-Si film is difficult to measure on an alkaline textured surface. Conventional optical techniques such as spectroscopic ellipsometry cannot be used due to the high scattering nature of the random pyramids. At poly-Si thicknesses below 50 nm, secondary electron microscopy (SEM) has difficulty distinguishing the poly-Si from the underlying c-Si substrate. Here, we demonstrate X-ray diffraction as an effective method to quantitatively measure the front poly-Si thickness. The thickness calculated from the diffraction peak height of the Si(111) crystallographic plane agrees well with the cross-section SEM analysis and simulations using SunSolve. We show that by thinning the front poly-Si from 200 to 60 nm, Jsc increased by 2.4 mA/cm2, while maintaining the same Voc. This led to an absolute efficiency gain of 1.73%. In addition, we also discuss possible reasons for the premature loss of passivation before the removal of all poly-Si, which prevented an even higher gain in Jsc.

National Renewable Energy Laboratory (NREL), Fraunhofer ISE

Kejun Chen and Alexandra Bothwell and Harvey Guthrey and Matthew B. Hartenstein and Jana Isabelle Polzin and Frank Feldmann and William Nemeth and San Theingi and Matthew Page and David L. Young and Paul Stradins and Sumit Agarwal

Solar Energy Materials and Solar Cells

Light/electron beam induced current,Parasitic absorption,Passivating contacts,Poly-Si/SiOx,Quokka,Scanning electron microscopy,Silicon solar cell,SunSolve simulation,XRD

2022

3

10.1016/J.SOLMAT.2021.111510

0927-0248

111510

North-Holland

236