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

Abstract

To optimize the optical response of a solar cell, specifically designed materials with appropriate optoelectronic properties are needed. Owing to the unique microstructure of doped nanocrystalline silicon oxide, nc-SiO x :H, this material is able to cover an extensive range of optical and electrical properties. However, applying nc-SiO x :H thin-films in photovoltaic devices necessitates an individual adaptation of the material properties according to the specific functions in the device. In this study, we investigated the detailed microstructure of doped nc-SiO x :H films via atom probe tomography at the sub-nm scale, thereby, for the first time, revealing the three-dimensional distribution of the nc-Si network. Furthermore, n-and p-type nc-SiO x :H layers with various optical and electrical properties were implemented as a window, back contact, and an intermediate reflector layer in silicon heterojunction and multi-junction thin-film solar cells with a focus on the key aspects for adapting the material properties to the specific functions. Here, nc-SiO x :H effectively reduced the parasitic absorption and opened new possibilities for the photon management in the solar cells, thereby, demonstrating the versatility of this material. Remarkably, using our adapted nc-SiO x :H layers in distinct functions enabled us to achieve a combined short circuit current density of 15.1 mA cm -2 for the two a-Si:H sub-cells in an a-Si:H/a-Si:H/µc-Si:H triplejunction thin-film solar cell and an active area efficiency of 21.4 % was realized for a silicon heterojunction solar cell.2

Silicon heterojunction solar cells: Recent technological development and practical aspects - from lab to industry

“…More promising might be the application of a two-phase material such as nanocrystalline silicon oxide (nc-SiO x :H). In such a material, a columnar nanocrystalline silicon phase providing vertical conductivity is embedded in an amorphous silicon oxide matrix providing enhanced transparency [60,61]. For nc-SiO x :H(n) at the front side of a SHJ solar cell, a slightly higher efficiency compared with an oxide-free nc-Si:H(n) reference is reported [62,63].…”

Doped hydrogenated nanocrystalline silicon oxide layers for high‐efficiency c‐Si heterojunction solar cells

“…Furthermore, nc‐Si:H alloyed with oxygen (nc‐SiO x :H) allows tunable optoelectrical properties, with the advantage of simultaneously obtaining higher E g and lower E a , when compared with a‐Si:H. This unique feature also enables more flexibility to tailor the selective transport for enhancing solar cells performance . Interestingly, with similar optical transparency, n‐type nc‐SiO x :H layers exhibit generally higher conductivity than p‐type layers . Accordingly, the use of p‐type nc‐SiO x :H as a front emitter in SHJ cell, which demands a more sensitive processing than n‐type counterpart, is rarely reported …”

“…6 Interestingly, with similar optical transparency, n-type nc-SiO x :H layers exhibit generally higher conductivity than p-type layers. 18,19 Accordingly, the use of p-type nc-SiO x :H as a front emitter in SHJ cell, which demands a more sensitive processing than n-type counterpart, is rarely reported. [20][21][22] On the other hand, in SHJ solar cell application, it is challenging to maintain an excellent electrical cell performance while optimizing the optical layer properties because of the substrate growth selectivity on top of the (i)a-Si:H layer.…”

Silicon Thin Films: Functional Materials for Energy, Healthcare, and IT Applications

“…It has been shown that doped microcrystalline silicon oxide has excellent optoelectronic properties for this application. This material was originally developed for use in thin‐film silicon solar cells, but its versatility as a functional material is clear. A “lab‐on chip” is a miniaturized system designed to perform bio‐analysis faster and more economically than a standard laboratory, at the point of use. Petrucci et al have integrated several of the functions required on to a single glass substrate, including a‐Si:H diode arrays that sense both light (proportional to short‐circuit current) and temperature (proportional to voltage when driven at constant dark current). A non‐volatile memory TFT was fabricated by Sanjeevi et al as a modification of a standard a‐Si:H TFT process.…”