The application of advanced nano and micro fabrication techniques on encapsulated layers to enhance the efficiency of thin film solar cells
Date Issued
2011
Date
2011
Author(s)
Tseng, De-Chen
Abstract
Thin film solar cells are widely studied and discussed because of their several advatages, such as low cost of materials, flexibility and tunable absorption band. However, the performance of thin film solar cells is limited by poor carrier mobility and insufficient absorption. Therefore one of the most important issues is increasing the effective absorption length and decreasing the thickness of thin film solar cells.
In this study, the harvest enhancement structures wewe designed on encapsulated layers of thin film solar cells. This design can avoid damaging the electronic properties of devices. Futhermore, the size of the structures would not be limited by the thickness of active layer. The light harvest enhancement structures are classified into two types of scattering by dielectric particles and diffraction gratings. This study reveals that the dielectric particles with larger refractive index and size possess better scattering effects. In the experiment, several kinds of dielectric particles are spun on an encapsulated layer. The polystyrene (PS) particles have better scattering ability than the SiO2 particles. The efficiency of solar cells was increased from 2.12% to 2.23% and reached the enhancement of 5.2% by coating the PS particles with a diameter of 722nm. Moreover, adding a high refractive index of TiO2 layer on the textured structures, the scattering ability increased and caused the efficiency increasing larger. Besides, we fabricated inverted pyramidial structures on a Polycarbonate (PC) substrate by the nanoimprint technique. The size of the inverted pyramidial structure is far more than the wavelength of incident light, so the behavior of light will be pridicted by geometric optics. The inverted pyramidial structure which possesses the ability of antireflection and 92% haze will increase the efficiency from 2.80% to 3.04% and the enhancement of current density reach 15%. Comparing to the scattering by nanoparticles, diffraction grating could lead to a large diffractive angle. When the period is smaller than the wavelength of incident light, the first-order diffractive angle will exceed the critical angle between air and the grating. And the light will be trapped in the active layer of a solar cell. The optimal structure is the triangle grating of polydimethylsiloxane (PDMS) which is coated by a high refractive index layer. Because this structure possesses excellent properties of antireflection and high diffraction efficiency, the absorption enhancement of an active layer will reach 106% at the wavelength of 700nm.
Subjects
thin film solar cells
light harvest enhanced structures
scattering by nanoparticles
diffraction grating
nanoimprint
soft lithography
autocloning technique
Type
thesis
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