Effects on the Surface and Luminescence Properties of GaAs by SF6 Plasma Passivation

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Abstract

The passivation effects of the SF6 plasma on a GaAs surface has been investigated by using the radio frequency (RF) plasma method. The RF’s power, chamber pressure, and plasma treatment time are optimized by photoluminescence (PL), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The PL intensity of passivated GaAs samples is about 1.8 times higher than those which are untreated. The oxide traps and As-As dimers can be removed effectively by using SF6 plasma treatment, and Ga-F can form on the surface of GaAs. It has also been found that the stability of the passivated GaAs surface can be enhanced by depositing SiO2 films onto the GaAs surface. These indicate that the passivation of GaAs surfaces can be achieved by using SF6 plasma treatment.

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Surface passivation effect by fluorine plasma treatment on ZnO for efficiency and lifetime improvement of inverted polymer solar cells

Ermioni Polydorou, Angelos Zeniou, Dimitris Tsikritzis … (2016)

The surface passivation effect of SF 6 plasma on ZnO films for application in polymer solar cells is demonstrated. Zinc oxide (ZnO) is an important material for polymer solar cells (PSCs) where the characteristics of the interface can dominate both the efficiency and lifetime of the device. In this work we study the effect of fluorine (SF 6 ) plasma surface treatment of ZnO films on the performance of PSCs with an inverted structure. The interaction between fluorine species present in the SF 6 plasma and the ZnO surface is also investigated in detail. We provide fundamental insights into the passivation effect of fluorine by analyzing our experimental results and theoretical calculations and we propose a mechanism according to which a fluorine atom substitutes an oxygen atom or occupies an oxygen vacancy site eliminating an electron trap while it may also attract hydrogen atoms thus favoring hydrogen doping. These multiple fluorine roles can reduce both the recombination losses and the electron extraction barrier at the ZnO/fullerene interface improving the selectivity of the cathode contact. Therefore, the fabricated devices using the fluorine plasma treated ZnO show high efficiency and stable characteristics, irrespective of the donor : acceptor combinations in the photoactive blend. Inverted polymer solar cells, consisting of the P3HT:PC 71 BM blend, exhibited increased lifetime and high power conversion efficiency (PCE) of 4.6%, while the ones with the PCDTBT:PC 71 BM blend exhibited a PCE of 6.9%. Our champion devices with the PTB7:PC 71 BM blends reached a high PCE of 8.0% and simultaneously showed exceptional environmental stability when using the fluorine passivated ZnO cathode interlayers.