Morphology Study of a Hybrid Structure Based on Porous Silicon and Polypyrrole
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0939-O03-22
Morphology Study of a Hybrid Structure Based on Porous Slicon and Polypyrrole Ma. Concepcion Arenas1, Hailin Hu1, J. Antonio del Río1, and M.E. Nicho2 1 Solar Materials, CIE-UNAM, Priv. Xochicalco S/N, Col. Centro, Temixco, Morelos, 62580, Mexico 2 CIICAp-UAEM, Cuernavaca, Morelos, Mexico
Abstract Double layer structures of porous silicon (PS) and polypyrrole (PPy) were prepared in order to study their electrical properties. PS was prepared by electrochemical etching in a HF/Ethanol solution from n-type silicon wafer and PPy by galvanstatic method in a lithium perchlorate/pyrrole solution. The experimental parameters for preparation of PS and PPy were varied to obtain different morphology of the PS/PPy structures. The surface topography of these structures was analyzed by Atomic Force Morphology (AFM). Tipand agglomerate-like morphologies of PPy were obtained on PS layers with different pore diameters. The electrical and AFM characterization of PS were studied with and without PPy. Current-voltage (I-V) curves of PS/PPy structures were obtained in dark and under illumination. PS without PPy ((+)Al/n-Si/PS/Cu(-)) shows an exponential behavior in the current, but it is almost linear when the PPy layer is deposited over the PS layer ((+)Al/nSi/PS-PPy/Cu(-)). All structures present photovoltage under illumination. However, this parameter is smaller in Al/n-Si/PS-PPy/Cu structure than Al/n-Si/PS/Cu. The open circuit voltage (VOC) and short circuit current density (JSC) of these structures decrease when the surface morphology of PPy is tip-like, but JSC increases when the surface morphology of PPy is agglomerate-like.
1. Introduction Since the discovery of porous silicon (PS) in 1990 [1], PS has kindled a broad range of experimental and theoretical investigations [2,3]. It also has been regarded as a promising material for optoelectronic applications [5-7]. The antireflection feature of PS has been approached in solar cell applications and it improves the performance of these devices. Due to the influence of the morphology and porosity of PS on any device application, the control of these parameters is quite important in PS device research and development. The high superficial area and tunable energy band gap of PS make it interesting for photovoltaic application studies. On the other hand, organic-inorganic hybrid heterojunctions have gained more attention for solar cell applications [8]. The use of
conducting polymers (CPs) has been an alternative to improve the stability and increase the effective conductivity of PS. This work presents a morphology study as well as the electrical characterization of PS-polypyrrole (PPy) structures.
2. Experimental Phosphorus-doped of crystalline silicon wafers (Czochralski, Atomergic Chemetals Corp.) with 10 Ohms-cm of resistivity and (100) orientation were used for the preparation of PS layers. The electrochemical etching was carried out at constant current density (20 or 50mA/cm2) in a HF(48wt%)/ethanol(98wt%) solution (1:1) during periods of 35s or 90s. During the
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