Modification of Surface Potential of Silicon by Organic Molecules

Abstract

The possibility of using an organic layer for controlling surface potential was investigated. The organic layer was formed by immersion in quinhydrone/methanol (QM) solution at room temperature. Surface passivation effects were estimated by lifetime measurements using the microwave photoconductive decay (m-PCD) method, and the surface condition was estimated by attenuated-total-reflection Fourier transform infrared (ATR-FTIR) measurement. Surface passivation effects due to the organic layer were clearly demonstrated. An increase in the lifetime of the wafer under illumination was observed. Charge trappings at the organic layer/silicon interface and in the organic layer were important for reducing surface recombination velocity. The organic layer can be formed at low temperature, and the formation process is simple. Hence, the application of an organic layer to silicon solar cells is expected for surface passivation films.

Examining the free radical bonding mechanism of benzoquinone– and hydroquinone–methanol passivation of silicon surfaces

“…While much work has been performed to demonstrate the efficacy of QHY/ME solutions, the mechanisms behind the high-quality passivation and the degradation of the effect once the passivated c-Si sample is removed from solution are still unknown [2,3,4,5,6,7,8,9]. Work on separate solutions of the constituent species of QHY have shown BQ/ME outperforms HQ/ME, but that HQ/ME passivated surfaces will improve given more than 3 hours of exposure to solution [6,10].…”

Wet Chemical Surface Passivation of Germanium Wafers by Quinhydrone–Methanol Treatment for Minority Carrier Lifetime Measurements

“…The effects of the surface recombination of minority carriers on both sides of Ge wafers should be suppressed to determine the value of b , as reported for the case of silicon (Si). [4][5][6][7][8] Although Gaubas and Vanhellemont 9) reported the dependence of b on the dopant concentration and carrier injection level in Ge, they did not describe the procedures of surface passivation of the Ge wafers. Posthuma et al 10) reported that the deposition of hydrogenated amorphous silicon (a-Si:H) by plasmaenhanced chemical vapor deposition (PECVD) is effective for passivating the surfaces of Ge wafers for the measurement of b .…”

“…However, the deposition of a-Si:H films is not suitable for routine and quick measurements of b . Wet chemical passivation utilizing iodine/alcohol 4) or quinhydrone/alcohol [5][6][7][8] treatment has been successfully applied to Si surfaces. Since these treatments are fairly simple and can be performed at room temperature (RT), they are useful for routine measurements of b in Si.…”

“…In particular, the quinhydrone/methanol (Q/M) treatment 6) developed by the present authors yields a low surface recombination velocity (S) of less than 5 cm/s, and the passivated Si surfaces are stable compared with those prepared by the iodine/alcohol treatment. The termination of Si dangling bonds by molecules from the Q/M solution and/or the trapping of electrons at the interface between the organic layer and the silicon substrate are possible mechanisms 8) for the passivation of Si surfaces by the Q/M treatment. The Q/M treatment has been used in the lifetime mapping of polycrystalline Si wafers.…”

“…The Q/M treatment has been used in the lifetime mapping of polycrystalline Si wafers. 6,7) However, this method has not yet been applied to Ge surfaces. Poelman et al 11) applied iodine solution for passivating the surfaces of low-resistivity Ge wafers, although they did not report the values of S.…”