Characterisation of intrinsic silicon oxide absorber layers for use in silicon thin film solar cells

Abstract

The use of a wide bandgap absorber layer in the top cell of a multi-junction silicon thin film solar cell is necessary to achieve a high-conversion efficiency. A higher bandgap of the absorber results in a higher open-circuit voltage (Voc) of the cell. In this work, intrinsic hydrogenated amorphous silicon oxide (i)a-SiO:H films have been prepared by using 13.56 MHz radio frequency plasma enhanced chemical vapour deposition (RF-PECVD) at a substrate temperature of 195 °C. The carbon dioxide (CO2) to silane (SiH4) ratio rc was varied and the influence of the ratio rc on the optoelectronic film properties was investigated. These thin films have been studied in detail in terms of their dark (σd) and photo (σph) conductivity and photoresponse PR (σph/σd). The defect density Nd and Urbach energy EU were determined by constant photocurrent method (CPM). The optical bandgap Eg,Tauc was derived from Tauc plots. Optical constants were determined by spectroscopic ellipsometry measurements in the range between 300 and 1000 nm. It was found that the increase in the CO2 to SiH4 ratio rc not only leads to a higher optical bandgap, but also higher defect density Nd and Urbach energy EU and on the other hand to a lower photoresponse PR. A suitable photoresponse PR = 8.64 × 105 at a high bandgap of Eg,Tauc = 1.91 eV and a defect density of Nd = 1.7 × 1016 cm−3 was achieved. The refraction index and extinction coefficient were lowered with increasing rc. The analysis of light-induced degradation in the (i)a-SiO:H layers showed a smaller increase of deep defects Nd and a higher increase of the Urbach energy EU in terms of the light soaking time with respect to the (i)a-Si:H reference layer

Realizing the Multiband Absorption in the Visible Region via the Collaboration of Fabry–Pérot, Propagating Surface Plasmons, and Void Plasmons Resonance Effects

“…In the next decade, various types of absorbers have been proposed. Most of these absorbers consist of a simple lattice structure in the top metal layer (arrays of gratings, [9][10][11][12][13] nanoparticles, [14][15][16][17][18][19][20][21][22][23][24][25][26] and nanoholes [27][28][29][30] ), an ultrathin dielectric middle layer, and a thick metal bottom layer. The absorption mechanism of these absorbers is to excite the coupling between the top metallic lattice structure and bottom metal layer, where the wavelength of absorption is related to the designed structures' fundamental mode.…”