Oliver Hohn

Excellent Silicon Surface Passivation Achieved by Industrial Inductively Coupled Plasma Deposited Hydrogenated Intrinsic Amorphous Silicon Suboxide

We present an alternative method of depositing a high-quality passivation film for heterojunction silicon wafer solar cells, in this paper. The deposition of hydrogenated intrinsic amorphous silicon suboxide is accomplished by decomposing hydrogen, silane, and carbon dioxide in an industrial remote inductively coupled plasma platform. Through the investigation on CO2 partial pressure and process temperature, excellent surface passivation quality and optical properties are achieved. It is found that the hydrogen content in the film is much higher than what is commonly reported in intrinsic amorphous silicon due to oxygen incorporation. The observed slow depletion of hydrogen with increasing temperature greatly enhances its process window as well. The effective lifetime of symmetrically passivated samples under the optimal condition exceeds 4.7 ms on planar -type Czochralski silicon wafers with a resistivity of 1 Ωcm, which is equivalent to an effective surface recombination velocity of less than 1.7 cms−1 and an implied open-circuit voltage () of 741 mV. A comparison with several high quality passivation schemes for solar cells reveals that the developed inductively coupled plasma deposited films show excellent passivation quality. The excellent optical property and resistance to degradation make it an excellent substitute for industrial heterojunction silicon solar cell production.

Investigation of Wide Process Temperature Window for Amorphous Silicon Suboxide Thin-Film Passivation Deposited by Inductively Coupled PECVD

Hydrogenated intrinsic amorphous silicon suboxide thin films deposited onto c-Si wafers by decomposing hydrogen, silane, and carbon dioxide in an industrial remote inductively coupled plasma tool are studied. Compared with intrinsic amorphous silicon deposited in the same tool, this material displays an improved process temperature window and excellent surface passivation quality, which is important for industrialization. The wide process window of over 200 °C (100 to 350 °C) mainly results from the slow depletion of H atoms at elevated temperature due to a suppressed epitaxial growth, whereas the excellent passivation quality is due to a much higher H content in the film compared with amorphous silicon. The temperature stability is further supported by a study using a high-resolution transmission electron microscopy. Under the optimal condition, the amorphous silicon suboxide demonstrates an effective minority carrier lifetime of over 4.7 ms on planar n-type 1-Ω · cm Czochralski silicon wafers, which is equivalent to an effective surface recombination velocity of less than 1.7 cm/s, and an implied open-circuit voltage of 741 mV.

Investigation of Low-Temperature Hydrogen Plasma-Etching Processes for Silicon Wafer Solar Cell Surface Passivation in an Industrial Inductively Coupled Plasma Deposition Tool

A hydrofluoric-acid (HF)-free hydrogen plasma dry etching process prior to the deposition of intrinsic amorphous silicon onto thin n-type planar Czochralski silicon wafers is developed. The influence of substrate temperature, hydrogen flow rate, and power density on the passivation quality is investigated. Advanced characterization using spectroscopic ellipsometry and transmission electron microscopy shows the impact of the etching conditions, especially the temperature and gas flow rates, on the surface quality and interface properties. It is found that the native oxide can only be removed effectively when wafers are subjected to higher temperature or lower hydrogen flow rate. The hydrogen, oxygen, and carbon concentration profiles at the a-Si/c-Si interface of the plasma-etched samples are studied and compared with the traditionally HF cleaned interface to gain a better understanding of the reasons for the superior passivation quality.

Inductively coupled plasma deposited amorphous silicon alloys using industrial equipment for heterojunction silicon solar cells

One of the most promising advanced solar cell designs for <; 100 μm thin silicon wafers is the heteroj unction silicon wafer solar cell (HET), with a very high efficiency potential with cost-effective low-temperature processing. In collaboration with German company Singulus Technologies and other industrial collaborators, SERIS is developing a pilot line suitable for mass production of HET cells. Initial experiments on the inductively coupled plasma deposition of a-Si:H(i) and compositionally similar alloy films such as a-SiOx:H(i) have yielded very good results compatible with high-voltage HET solar cells, with the passivation quality of a-SiOx:H(i) being consistently higher, and far less sensitive to the deposition temperature compared to a-Si:H(i). In fact, a-SiOx:H(i) has a stable process window of more than 200°C that is suitable for the production environment. The wider process window can be attributed to suppressed epitaxial growth and incubation layer thickness in the a-SiOx:H(i) layer at high deposition temperatures.