Silicon surface passivation by polystyrenesulfonate thin films

Abstract

The use of polystyrenesulfonate (PSS) thin films in a high-quality passivation scheme involving the suppression of minority carrier recombination at the silicon surface is presented. PSS has been used as a dispersant for aqueous poly-3,4-ethylenedioxythiophene. In this work, PSS is coated as a form of thin film on a Si surface. A millisecond level minority carrier lifetime on a high resistivity Si wafer is obtained. The film thickness, oxygen content, and relative humidity are found to be important factors affecting the passivation quality. While applied to low resistivity silicon wafers, which are widely used for photovoltaic cell fabrication, this scheme yields relatively shorter lifetime, for example, 2.40 ms on n-type and 2.05 ms on p-type wafers with a resistivity of 1–5 Ω·cm. However, these lifetimes are still high enough to obtain high implied open circuit voltages (Voc) of 708 mV and 697 mV for n-type and p-type wafers, respectively. The formation of oxides at the PSS/Si interface is suggested to be responsible for the passivation mechanism.

Temporary Surface Passivation for Characterisation of Bulk Defects in Silicon: A Review

“…Following on from the PEDOT:PSS work, Chen et al examined the passivation quality of PSS after a short 130 °C heat‐treatment . Very low S values of 0.65–7 cm s −1 were attained when the PSS films were exposed to an oxygen ambient, however S increased dramatically when exposed to either nitrogen or ambient air conditions, which is clearly problematic from a materials characterisation perspective.…”

“…In contrast to PEDOT:PSS, Chen et al investigated the passivation mechanisms of PSS when in contact with silicon . The initial requirement for a high level of surface passivation is a H‐terminated silicon surface.…”

“…The initial requirement for a high level of surface passivation is a H‐terminated silicon surface. When the PSS film is deposited on the silicon surface, thermal equilibrium must be satisfied, in which case the bands bend downwards in n‐type silicon, thus forming accumulation of electrons at the silicon surface . Prior to exposing the PSS film to an oxygen ambient, the silicon surface is moderately passivated by the PSS film, however in the presence of oxygen, excellent surface passivation is attained.…”

“…In contrast, there have been a number of trialled wet chemical pre‐treatment processes, however the favored treatment to‐date is a simple HF dip to remove any native oxide prior to deposition. This simple treatment prior to thin film passivation has led to some very low S values of 3–10 cm s −1 , and in one case a very low S of 0.65 cm s −1 , however the later was achieved on near intrinsic silicon. While low S have been achieved without substantial wet chemical pre‐treatment processing, a simple HF dip is susceptible to an unreliable surface condition by either surface contamination from previous wet chemical processing or the surface morphology (etched versus polished).…”

Superacid-Treated Silicon Surfaces: Extending the Limit of Carrier Lifetime for Photovoltaic Applications

“…Omission of the conducting polymer PEDOT has led to This work is licensed under a Creative Commons Attribution 3.0 License. For more information, see http://creativecommons.org/licenses/by/3.0/ Chen et al demonstrating a high level of surface passivation by depositing just PSS, which after a short heat-treatment at 130°C for 10 min yields iV oc of 700-710 mV and S of 4-5 cm/s on nand p-type silicon [16]. While PEDOT: PSS and PSS films are promising approaches to contacting or passivating silicon, they do exhibit severe degradation under ambient conditions, and thus require capping films in order to inhibit degradation [13].…”