HF etched glass substrates for improved thin-film solar cells.

A hemisphere-array textured glass substrate was fabricated for the development of an improved thin-film (TF) silicon solar cell. The HF-H2SO4-etchant system influenced the light path owing to the formation of the strong fluorine-containing HSO3F acid. In particular, the etching system of the various HF concentration with a constant H2SO4 solution is related to make an improvement of optical transmittance and light trapping structure without a uniform pattern. According to the specular transmittance measurements, the haze ratio was maintained for the glass sample etched with 35% HF in the longer-wavelength region. The proposed substrate was implemented in a TF-Si solar cell, and an improved conversion efficiency was observed according to the short-circuit current density owing to the increase in the haze ratio. This morphology, therefore, induces more scattering at the front side of the cell and leads to an improvement of the open circuit voltage gain for the HF 25% cell. It will be helpful to understand the application of thin film solar cell based on the HF-H2SO4 etching system for the readers.

High Efficiency Inorganic/Inorganic Amorphous Silicon/Heterojunction Silicon Tandem Solar Cells.

We investigated high-efficiency two-terminal tandem photovoltaic (PV) devices consisting of a p/i/n thin film silicon top sub-cell (p/i/n-TFS) and a heterojunction with an intrinsic thin-layer (HIT) bottom sub-cell. We used computer simulations and experimentation. The short-circuit current density (Jsc) of the top sub-cell limits the Jsc of the p/i/n-TFS/HIT tandem PV device. In order to improve the Jsc of the top sub-cell, we used a buffer-layer at the p/i and i/n interface and a graded forward-profile (f-p) band gap hydrogenated amorphous silicon germanium active layer, namely i-layer, in the top sub-cell. These two approaches showed a remarkable raise of the top sub-cell's Jsc, leading to the increase of the Jsc of the PV tandem device. Furthermore, in order to minimize the optical loss, we employed a double-layer anti-reflective coating (DL-ARC) with a magnesium fluoride/indium tin oxide double layer on the front surface. The reduction in broadband reflection on the front surface (with the DL-ARC) and the enhanced optical absorption in the long wavelength region (with the graded f-p band gap) resulted in the high Jsc, which helped achieve the efficiency up to 16.04% for inorganic-inorganic c-Si-based tandem PV devices.

Study of low resistivity and high work function ITO films prepared by oxygen flow rates and N2O plasma treatment for amorphous/crystalline silicon heterojunction solar cells.

Pulsed DC magnetron sputtered indium tin oxide (ITO) films deposited on glass substrates with lowest resistivity of 2.62 x 10(-4) Ω x cm and high transmittance of about 89% in the visible wavelength region. We report the enhancement of ITO work function (Φ(ITO)) by the variation of oxygen (O2) flow rate and N2O surface plasma treatment. The Φ(ITO) increased from 4.43 to 4.56 eV with the increase in O2 flow rate from 0 to 4 sccm while surface treatment of N2O plasma further enhanced the ITO work function to 4.65 eV. The crystallinity of the ITO films improved with increasing O2 flow rate, as revealed by XRD analysis. The ITO work function was increased by the interfacial dipole resulting from the surface rich in O- ions and by the dipole moment formed at the ITO surface during N2O plasma treatment. The ITO films with high work functions can be used to modify the front barrier height in heterojunction with intrinsic thin layer (HIT) solar cells.