Wide Gap Microcrystalline Silicon Oxide Emitter for a-SiO_x:H/c-Si Heterojunction Solar Cells

Abstract

This paper reports on the development of phosphorous doped microcrystalline silicon oxide (µc-SiO x :H) films as an emitter window layer in flat p-type silicon heterojunction (SHJ) solar cells featuring intrinsic a-SiO x :H buffer layers. We investigated the material properties of n-type µc-SiO x :H films grown at various input gas ratios and correlated the results of SHJ solar cells utilizing varying oxygen content and thickness of the emitter layer to the corresponding film properties. A maximum efficiency of 19.0% was achieved. The excellent short circuit current of 35.8 mA/cm2 for flat cells was attributed to the low optical losses in the emitter window.

Versatility of doped nanocrystalline silicon oxide for applications in silicon thin-film and heterojunction solar cells

“…1 a)). The main focus in this application is to reduce the parasitic absorption at the front of the solar cell due to the high transparency of nc-SiO x :H layers in comparison to a-Si:H [8,15,21]. At the same time, the conductivity of the employed layers has to be sufficient to maintain a high fill factor (FF) in the device.…”

“…The distribution of nc-Si was similar for both films, although the volume fraction of nc-Si was less in the p-type material. The lower crystallinity of the p-type material is probably related to the amorphization effect by the B [8,13,35,36].…”

“…Particularly, the optical and electrical properties of this material can be varied in a broad range, providing a tunable refractive index, a low absorption coefficient in the relevant energy range, and a sufficient electrical conductivity. This is made possible by its characteristic microstructure, which is usually described as comprising of well conducting filaments or pearl-chain like arrangements of nanocrystalline silicon (nc-Si) embedded in a highly transparent, oxygen rich amorphous silicon oxide (a-SiO x :H) matrix as indicated by TEM investigations [1,2,7,8]. As a result, nc-SiO x :H is widely applicable as a window, back contact (BC) or intermediate reflector (IR) layer in various solar cell concepts.…”

Applications of Oxide Coatings in Photovoltaic Devices

“…Since amorphous silicon (a-Si:H) strongly absorbs blue photons, silicon sub-oxides have been explored to replace it in HIT cells. Recent investigations include replacement of the amorphous silicon (a-Si:H) emitter with doped amorphous hydrogenated silicon oxide a-SiO x :H and doped hydrogenated microcrystalline silicon oxide (μc-SiO x :H) [73,74]. On the other hand, doped amorphous hydrogenated silicon oxide a-SiO x :H has been used as an alternative to a-Si:H as a passivation layer [75].…”

Improved hetero-interface passivation by microcrystalline silicon oxide emitter in silicon heterojunction solar cells

“…lc-Si x :H layer has tunable refractive index and optical band gap [14][15][16]. During the past years, lc-SiO x :H has successfully attracted considerable attention owing to its outstanding optical properties and high electrical conductivity.…”