Abstract
Improvement of solar-cell efficiency at a minimum possible cost addition is constantly sought, and this is often achieved at incremental percentage steps. Among a number of alternatives, antireflective coatings and surface texturing are the most prominent. This paper presents an alternative texturing method of crystalline silicon in an attempt to improve the efficiency of photon transmission through the surface and collection in the bulk. The method relies on anisotropic etching of bulk silicon and requires only a single oxide mask and two etching steps with a KOH or TMAH aqueous solution. The surface texture consists of smooth hemispherical cavities, which do not demand a lithographic mask or intricate technology processes to obtain the hemispherical cavities. This method can be applied to increase the profile area of the originally flat frontal surface exposed to light and consequently increase the effective width of the depletion region. The latter implies a higher probability of photon collection, contributing to the improvement of the conversion efficiency of the device. The textured nontilted silicon solar-cell transmittance under small solar incidence angles at dawn and sunset is improved compared to a flat surface, increasing the photocurrent.
Highlights
Very often texturing is employed to increase the solar-cell surface area [1, 2]
The overall efficiency of a solar cell depends on several aspects, among which, the composition of the semiconductor, temperature, contacts and metallization, antireflection coatings (ARC) type, doping concentration and topology of the cell layers, and encapsulation
In this paper we focus primarily on this alternative texturing idea, and present a preliminary performance analysis based on the influence of the proposed texturing on the transmittance at the air-silicon interface, representing the portion of the solar radiation effectively penetrating the cell bulk
Summary
Very often texturing is employed to increase the solar-cell surface area [1, 2]. In some methods, based on inverted pyramids or laser-induced cone-shaped pillars, internal optical confinement of long-wavelength photons can be enhanced by light trapping [3, 4]. We present a method to texture the silicon surface to improve optical transmittance into the cell, especially at low sun-elevation angles. In this method a mesh of pyramidal pits in silicon gradually evolves into a mesh of hemispherical cavities by means of a single-step anisotropic etching with a KOH aqueous solution [8]. For each particular case, a detailed full-cycle cost evaluation needs to be done This first unambitious analysis might, notwithstanding its primitiveness, incite alternative ideas, based on the proposed technology, either for commodity or custom photovoltaic cells, and propel more in-depth research in this direction
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