Investigation of a-Si:H solar cells with a protocrystalline-like amorphous silicon intrinsic layer
We investigate the effects of the hydrogen dilution in a-Si:H film on the crystallization and the absorption property. Crystallization of the a-Si:H films from amorphous to several tens nanometer-sized crystal state is observed by increase of hydrogen dilution ratio using PECVD. The phase transition of the a-Si:H films from amorphous to micro-crystal occurred very rapidly in a very narrow range of the silane concentration(SC). Protocrystalline-like properties of silicon (pc-Si:H) is obtained fractionally within the a-Si:H matrix. It could be assumed that the volume fraction of the protocrystalline silicon is the highest in the range of SC=3.7∼4.0%, whereas amorphous or micro-crystalline phases are dominant in the other range of SC<4.0% and SC>3.0%, respectively. The μc-Si:H films with SC=1.0%~1.4% have the micro-crystalline volume fraction 75%∼80%. But the μc-Si:H films still contain the amorphous, proto- or nano-crystalline silicon in the rest volume so that they show some different characteristics with other micro-crystalline silicon. The a-Si:H films with SC=3.7∼4.0% doesn't contain the micro-crystalline volume fraction but different characteristics in absorption from the other a-Si:H films with higher SC>4.0%. Such films could be assumed to have the properties of the protocrystalline silicon. They, consequently, showed the low degradation property from the light soaking and the rapid stability.
Hot-wire chemical vapor-deposited microcrystalline silicon in single and tandem n–i–p solar cells
Abstract This paper examines the potential of μc-Si deposited by hot-wire chemical vapor deposition (HWCVD) at a constant hydrogen dilution of 0.95, as absorber layer in n–i–p thin film solar cells. For a series of single junction cells onto plain stainless steel, the highest open circuit voltage (Voc) and Fill Factor (FF) were 0.54 V and 0.72. From J–V measurements at reduced light intensities, the change of the AM1.5-normalized FF values with light intensity was found to depend on the μc-Si i-layer thickness. This is attributed to the thickness evolution of the i-layer crystallinity, which influences the cell properties, particularly for i-layers thinner than 2.0 μm. For thicker layers the measurements clearly show drift-driven charge carrier collection. Tandem cells showed FF values as high as 0.77, which indicates the very high optoelectronic quality of the μc-Si material. A 2.0 μm cell on a textured back reflector shows an efficiency of 7.8%.
Microstructure of amorphous and microcrystalline Si and SiGe alloys using X-rays and neutrons
This review describes recent experimental applications of small-angle X-ray (SAXS) and neutron scattering, as well as X-ray diffraction (XRD), for the determination of the microstructure of relevant solar cell thin film materials based on hydrogenated amorphous Si and SiGe alloys. Due to the recent trend toward use of amorphous Si and SiGe materials prepared near the onset of microcrystallinity, this review also describes the use of XRD to detect and determine the role of medium-range order and partial microcrystallinity in solar cell behavior. Some recent results from SAXS and XRD applied to microcrystalline Si are also summarized.