Evaluation of Process Damage Induced by Sputtering of Transparent Conductive Oxide Films for Crystalline Silicon Solar Cells

Abstract

We evaluated the damage to crystalline silicon caused by sputtering deposition of transparent conductive oxide films (TCO). We confirmed that direct deposition of TCO on the crystalline silicon deteriorates the carrier lifetime. Also, the difference in discharge voltage during the TCO sputtering has an influence on plasma damage and damage penetration depth to the crystalline silicon. We consider that the carrier lifetime is reduced because of the surface recombination posed by the damage. Furthermore, photoluminescence (PL) spectroscopy was performed, and the so-called “irradiation-induced defects,” defects that are formed typically after electron beam and ion irradiation, were observed at deep levels of 0.789 eV, 0.767 eV, and 0.714 eV. These irradiation-induced defects act as recombination centers and may cause the deterioration of the conversion efficiency in crystalline silicon solar cells. We believe understanding and controlling these defects are important for improving the conversion efficiency of solar cells.

Evaluation of Damage in Crystalline Silicon Substrate Induced by Plasma Enhanced Chemical Vapor Deposition of Amorphous Silicon Films

“…Damage to c-Si from sputtering and reactive plasma deposition (RPD) methods has resulted in luminescent defects such as C-lines (Ci-Oi complex) which are detected by PL measurement. 14,15 The I TO intensity and edge emission after a-Si deposition were slightly stronger than that from the original substrate within a variation of repeatability. These defects are formed by the relatively large ion impact energy of oxygen and argon on c-Si.…”

“…The carrier lifetime of the sample after deposition and Si substrate after etching with quinhydrone methanol passivation were comparable to that in previous studies. 15,[26][27][28] We define the damaged layer as the period between the increase in carrier lifetime and its convergence to a constant. Approximately 2.8 nm from the c-Si surface, we observed the damaged layer which was estimated from the number of cycles required for etching from an increase in carrier lifetime to converge to a constant value.…”

“…These defects are formed by the relatively large ion impact energy of oxygen and argon on c-Si. 15 As shown in Table III, ion bombardment during deposition is a concern for the PECVD method as well as the sputtering and RPD methods. However, the collision energy was relatively small, and luminescence defects such as Clines, which were observed in the sputtering deposition, were not observed.…”

“…In addition, degradation of solar cells due to damage that occurs during the manufacturing process has been also reported. 14,15 For example, damage to the Si substrate has been reported in PECVD of amorphous hydrogenated silicon nitride (SiN x ), which is deposited as an antireflection film. 16 Such damage causes an increase in recombination centers and defects within c-Si, leading to a decrease in carrier lifetime.…”

ZnO‐Doped In2O3 Front Transparent Contact Enables >24.0% Silicon Heterojunction Solar Cells

“…While the sputtering process would induce damage to intrinsic amorphous silicon layer and reduce the passivation quality, this damage can be lowered by working with higher temperatures. [23,24] Therefore, the substrate temperature can not only modulate the optoelectrical properties of IZO films, but also reduce the sputtering damage through the in situ annealing treatment at high substrate temperature.…”