Highly conductive microcrystalline n-layers for amorphous silicon stacked solar cells: preparation, properties, and device application

Highly conductive n-type microcrystalline (μc) silicon layers were deposited by conventional 13.56 MHz PECVD in a commercial multichamber deposition system for amorphous silicon solar cells. A conductivity up to 80 (Ω cm)^-1 was obtained. In addition to optical and Raman characterization, the film structure was analyzed by TEM and electron diffraction, revealing a tight assembly of near-spherical clusters of ≈100 nm size, which are built up from smaller crystallites. Information on the process recipe to be used in stacked cells was obtained from the use of μc n-layers in pin cells, and by depositing thin μc films on thick amorphous layers, which permits to determine the conductivity for device-relevant conditions. A strongly reduced n-p contact resistance was found in comparison to amorphous n-p contact systems. The prepared pinpin stacked cells employing the μc films exhibit improved fill factors of up to 75% and an improved short-circuit current as compared to the ones with amorphous n-layers in the inner n-p contact