Understanding of Molecular Contribution of Quinhydrone/Methanol Organic Passivation for Improved Minority Carrier Lifetime on Nanostructured Silicon Surface

Abstract

In this report, we present a study of the quinhydrone/methanol (QHY/MeOH) organic passivation technique for a silicon (Si) surface. The roles of p-benzoquinone (BQ) and hydroquinone (HQ), which make up QHY, in controlling the uniformity and coverage of the passivation layer as well as the minority carrier lifetime (τeff) of Si were investigated. The uniformity and coverage of the passivation layer after treatment with diverse mixture ratios of BQ and HQ in MeOH were studied with two different atomic force microscope (AFM) techniques, namely tunneling mode (TUNA) and high-resolution tapping mode AFM (HR-AFM). In addition, the τeff and surface potential voltages (SPV) of passivated surfaces were measured to clarify the relationship between the morphologies of the passivation layers and degrees of surface band bending. The molecular interactions between BQ and HQ in MeOH were also analyzed using Fourier-transform infrared spectroscopy (FT-IR). In our study, we successfully demonstrated the role of each molecule for effective Si surface passivation with BQ working as a passivation agent and HQ contributing as a proton (H+) donator to BQ for accelerating the passivation rate. However, our study also clearly revealed that HQ could also hinder the formation of a conformal passivation layer, which raises an issue for passivation over complex surface geometry, especially a nanostructured surface.

Photovoltaic Device Application of a Hydroquinone-Modified Conductive Polymer and Dual-Functional Molecular Si Surface Passivation Technology

“…Moreover, as proven in our previous study, the Si-SQ bond also results in the formation of an intramolecular dipole moment owing to the difference in polarity between the O-H group and the oxygen atoms present at both ends of SQ. This arrangement induces upward band bending at the Si surface, as shown in Figure 8c [66]. This upward band-bending with SQ can lead to an imbalance in the carrier concentration between electrons and holes on the Si surface, eventually lowering the surface recombination velocity and thus providing effective field effect passivation for the Si surface.…”

“…This made it necessary to consider two factors: (1) the formation of a passivation layer for excessive Si surface defect states and (2) improvement of the wettability of the PEDOT:PSS solution on the Si surface. Towards this purpose, we developed the technology to introduce benzoquinone (BQ) for Si surface passivation during HSC fabrication [66]. Figure 8 depicts the use of BQ to passivate the unsaturated-Si atoms on the Si surface.…”

“…As shown in Figure 8a, BQ acts as an oxidation agent for MeOH when mixed with this solvent and transforms one of the carbonyl groups of BQ into a hydroxyl O-H group by acquiring a H + from MeOH. BQ is then transformed into the semiquinone (SQ) molecule [66,67]. Upon immersion of the HF-cleaned Si substrate into the prepared BQ/MeOH passivation solution containing these SQ molecules, Si-SQ bonds are formed between unsaturated-Si atoms on the Si surface and the oxygen atom with an unpaired electron of SQ, as shown in Figure 8b.…”