Abstract
Porous-silicon (PS) multi-layered structures with three stacked PS layers of different porosity were prepared on silicon (Si) substrates by successively tuning the electrochemical-etching parameters in an anodization process. The three PS layers have different optical bandgap energy and construct a triple-layered PS (TLPS) structure with multiple bandgap energy. Photovoltaic devices were fabricated by depositing aluminum electrodes of Schottky contacts on the surfaces of the developed TLPS structures. The TLPS-based devices exhibit broadband photoresponses within the spectrum of the solar irradiation and get high photocurrent for the incident light of a tungsten lamp. The improved spectral responses of devices are owing to the multi-bandgap structures of TLPS, which are designed with a layered configuration analog to a tandem cell for absorbing a wider energy range of the incidental sun light. The large photocurrent is mainly ascribed to an enhanced light-absorption ability as a result of applying nanoporous-Si thin films as the surface layers to absorb the short-wavelength light and to improve the Schottky contacts of devices. Experimental results reveal that the multi-bandgap PS structures produced from electrochemical-etching of Si wafers are potentially promising for development of highly efficient Si-based solar cells.
Highlights
Since the report of room temperature photoluminescence in porous silicon (PS) [1], this material has been extensively investigated for the development of optoelectronic devices
We report the preparation and characterization of triple-layered PS (TLPS) structures and demonstrated the improvements on the spectral photoresponses and light-absorption capability of Si-based photovoltaic devices fabricated with the developed TLPS structures
It can be observed that a triple-layered structure with an NPS, an HP-PS and a low-porosity PS (LP-PS) layer stacking from top to bottom are formed on a Si substrate
Summary
Since the report of room temperature photoluminescence in porous silicon (PS) [1], this material has been extensively investigated for the development of optoelectronic devices. Because each semiconductor material is sensitive to a different part of the solar spectrum, tandem cells can obtain enhanced overall sunlight photoresponses and achieve higher conversion efficiency. Based on the fact that a PS layer of higher porosity has higher bandgap energy, a PSML structure composed of triple stacking layers with high-, medium- and low-porosity (from top to bottom) will absorb the sun light in the short-, medium- and long-wavelength bands respectively. Such a “tandem-like” PSML structure can potentially harvest a broader range of the sun’s energy to make a Si-based solar cell more efficient. We report the preparation and characterization of TLPS structures and demonstrated the improvements on the spectral photoresponses and light-absorption capability of Si-based photovoltaic devices fabricated with the developed TLPS structures
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