Effects of Ion Bombarding and Nitrogenation on the Properties of Photovoltaic a-CN x Thin Films
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Effects of Ion Bombarding and Nitrogenation on the Properties of Photovoltaic a-CNx Thin Films Z.B. Zhou * , R.Q. Cui, G.M. Hadi, Q.J. Pang Solar Energy Institute, Department of Physics, Shanghai Jiaotong University, Shanghai 200030 China C.Y. Jin, Z. M. Ding Instrumental Analysis Center, Shanghai Jiaotong University, Shanghai 200030 China ABSTRACT Amorphous carbon nitride films (a-CNx) were synthesized by using single ion beam sputtering of a graphite target in argon and nitrogen sputtering gases. This thin film could be used as a novel photovoltaic material. The films were characterized with the technique of laser Raman, spectroscopic ellipsometry and electron spin resonance spectrometer (ESR). In this paper we report the effects of ion impacting and nitrogenation on the microstructure, density of defect states, bonding character, optical and photovoltaic properties. Effective decreasing of intensity of the ESR signal and formation of C-N bonding were observed, which could be attributed to the increment of the impinging ions on the growing films. The nitrogenation of a-CNx films could decrease the Tauc optical gap (0.62~0.86eV) and the intensity of ESR signal, increase photon absorption coefficient of the films (106~104cm-1). The primary photovoltaic values of the devices having Schottky structure of ITO/CNx/Al are Isc 1.56 A/cm2 and Voc 250 mV, respectively, when exposed to AM1.5 illumination ( 100mW/cm2, 25 ).
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INTRODUCTION The interest in carbon nitride thin films was referred to the theoretical calculation of its possible crystal structure –C3N4 in 1980s [1,2]. This crystalline alloy is claimed in the ranking of hardest materials. Since that time, many efforts have carried out to synthesis this new crystal material with less success [3]. Actually, the carbon nitride films with amorphous structure might be a rather promising novel electronic material considering its electrical, optical properties can be controlled by changing the concentration of nitrogen atoms in the thin films or by choosing different deposition processes [3,4]. This new material possesses some peculiar properties, such as negative electron affinity, low dielectric constant and high photoconductive gain, so it could be used on field emitting displays, interlayer of integration circuits and photovoltaic devices [5-7]. The synthesis of carbon nitride films can be achieved with variety techniques, such as plasma enhanced CVD [8,9], unbalanced magnetron sputtering [10], ion-beam deposition [11], laser ablation and FCVA [12,13]. In all of these processes, the ion bombardment during the deposition is one of the most important factors, which affects the bonding structure, electronic and optical properties of thin films. In this work, the films we studied were deposited by the method of single ion beam sputtering process (SIBS). We mainly studied the effects of ion bombardment and nitrogenation processing conditions on the properties of the
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amorphous carbon nitride thin films for photovoltaic application. We adjusted the amount of
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