High‐rate deposition of microcrystalline silicon in a large‐area PECVD reactor and integration in tandem solar cells

Abstract

We study the high-rate deposition of microcrystalline silicon in a large-area plasma-enhanced chemical-vapor-deposition (PECVD) reactor operated at 40.68 MHz, in the little-explored process conditions of high-pressure and high-silane concentration and depletion. Due to the long gas residence time in this process, the silane gas is efficiently depleted using moderate feed-in power density, thus facilitating up-scaling of the process to large surfaces. As observed in more traditional deposition processes, the deposition rate and performance of device-quality material are limited by the inter-electrode gap of the reactor. We significantly increase the cell performances by reducing this gap. X-ray diffractometry (XRD) and secondary ion mass spectroscopy (SIMS) are used to characterize the microcrystalline material deposited in the modified reactor at a rate of 1 nm/s. Comparison with a microcrystalline process at a low deposition rate demonstrates that the crystallographic orientation of the absorbing layer of the cell and the concentrations of contaminants are strongly correlated and dependent on the process. We use microcrystalline cells with absorber layer grown at a rate of 1 nm/s integrated as bottom cells in amorphous-microcrystalline (micromorph) tandem solar cells using the superstrate configuration. We report an initial efficiency of 10.8% (9.6% stabilized) for a tandem cell with 1.2 cm 2 surface.

The effect of pretreatment for SiH4 gas by microwave plasma on Si film formation behavior by thermal CVD

“…This value appears to be extremely high in comparison with that of a Si film deposited in a conventional PECVD system because the SiH 4 residence time in the low‐pressure plasma CVD is generally on the order of seconds. [ 35,36 ] Therefore, a higher plasma density could be obtained by our microwave plasma compared with the low‐pressure plasma.…”

“…This value appears to be extremely high in comparison with that of a Si film deposited in a conventional PECVD system because the SiH 4 residence time in the low-pressure plasma CVD is generally on the order of seconds. [35,36] Therefore, a higher plasma density could be obtained by our microwave plasma compared with the low-pressure plasma. Figure 6 shows a typical optical emission spectrum obtained from the plasma during plasma treatment at a Q H 2 of 10 SLM, Q SiH 4 of 10 sccm, W μW of 600 W, and P total of 20 Torr.…”

Nearly Perfect Polycrystalline, Large-Grained Silicon Arrays Formed at Low-Temperature Ambient by Local Pyrolysis

“…4 Device-grade p-Si can be grown at even lower substrate temperatures (e.g., 300 °C) when using other energy sources such as plasma, hot wires, and lasers. Very-highfrequency-plasma-enhanced chemical vapor deposition 5 (VHF-PECVD) or hot-wire chemical vapor deposition 6 (HW-CVD) are actively developed to grow p-Si for solar cells. Another approach to make p-Si is excimer-laser 7 or electric-field 8 driven crystallization of amorphous silicon (a-Si), 9 used with TFTs in active matrix organic light-emitting diodes.…”

Polarized Raman Spectroscopy and Chemometric Analysis of Micro-crystalline Silicon for Solar Cells

“…It has a higher doping efficiency requiring less Hydrogen than amorphous hydrogenated Si (a-Si:H) so is resistant to the Staebler-Wronski effect and has increased absorption efficiency at longer wavelengths than a-Si:H [1]. It has strong potential in multijunction solar cells.…”