In-situ CVD processes for crystalline silicon thin-film solar cells

Abstract

The aim of this paper is to present in-situ and cost-effective processes for crystalline silicon thin-film solar cells grown by high-temperature chemical vapour deposition on low-cost silicon substrates. The central approach is the epitaxial wafer-equivalent (EpiWE) cell structure, consisting of an epitaxial layer deposited on a low-cost silicon substrate. This EpiWE is then processed using a standard wafer solar cell process. Novel in-situ chemical vapour etching (CVE) and deposition (CVD) processes extend this concept to a nearly completed solar cell, the `EpiCell'. These processes enable the use of substrates produced from slightly purified metallurgical silicon and result in efficiencies potentially as high as for standard multicrystalline wafers. The results show that the saw damage can easily be removed by etching the samples at high temperatures with HCl gas. Gettering of highly contaminated substrates reduces the amount of impurities by up to 80%. This is the first time that the gettering effect of HCl gas diluted in hydrogen for PV application is demonstrated. By porosification of the substrates and texturing the front side, the incident light is confined in the deposited layer. The epitaxial growth allows the fabrication of high efficiency emitters resulting so far in solar cell efficiencies up to 15.2% on Cz substrates (92 cm2). A front side texture by HCl etching shows a diffuse fraction of nearly 90% of the spectral reflectance. All these processes can be transferred to the newly designed ProConCVD, our high-throughput in-line CVD tool

Efficiency (>15%) for thin‐film epitaxial silicon solar cells on 70 cm2 area offspec silicon substrate using porous silicon segmented mirrors

“…And as such, a high throughput, continuous CVD (ConCVD) reactor prototype was developed [2] at Fraunhofer Institute for Solar Energy Systems (ISE, Germany), with a throughput of 1 m 2 /h of Si deposition. As reported by Ref [3]. the proof of concept of ConCVD reactor was shown by the fabrication of epitaxial silicon solar cells with efficiencies of 12Á5%.…”

“…The front side contacts were defined by photolithography, followed by a sequence of Ti/Pd/Ag (30/30/100 nm) evaporation and silver electroplating to increase the thickness up to 10-20 mm. A DARC of 50 nm TiO 2 and 105 nm MgF x was applied to the solar cells, increasing the short-circuit current density and therefore efficiency by factor of 1Á4 [3].…”

“…Figure 4 shows an SR-LBIC (spectrally resolved light beam induced current measurement) map of the best solar cell with segmented chirped reflector. In this technique, the J sc and reflection of the contacted solar cell are simultaneously measured during the laser beam scan; and the effective diffusion length can be locally determined for different wavelengths depending on the desired depth resolution [3]. In Figure 4, the middle area of the solar cell (approx.…”

Effects of process conditions for the n⁺-emitter formation in crystalline silicon

“…The second alternative to the diffusion process is the emitter formation by epitaxial growth using CVD (chemical vapour deposition) at temperature ranges >1000°C [12]. The highly doped layer thereby grows with a very high growth rate (30 times faster than the POCl 3 diffusion process).…”

Junction Formation With HWCVD and TCAD Model of an Epitaxial Back-Contact Solar Cell

“…Silicon epitaxy is a well known process in microelectronics and thin film solar cells [4]- [6]. However it is regarded as a novel process in bulk crystalline silicon photovoltaics.…”