Search

Amorphous/crystalline silicon interfaces feature considerably larger valence than conduction band offsets. In this article, we analyze the impact of such band offset asymmetry on the performance of silicon heterojunction solar cells. To this end, we use silicon suboxides as passivation layers-- inserted between substrate and (front or rear) contacts--since such layers enable intentionally exacerbated band-offset asymmetry. Investigating all topologically possible passivation layer permutations and focussing on light and dark current-voltage characteristics, we confirm that to avoid fill factor losses, wider-bandgap silicon oxide films (of at least several nanometer thin) should be avoided in hole-collecting contacts. As a consequence, device implementation of such films as window layers--without degraded carrier collection--demands electron collection at the front and hole collection at the rear. Furthermore, at elevated operating temperatures, once possible carrier transport barriers are overcome by thermionic (field) emission, the device performance is mainly dictated by the passivation of its surfaces. In this context, compared to the standard amorphous silicon layers, the wide-bandgap oxide layers applied here passivate remarkably better at these temperatures, which may represent an additional benefit under practical operation conditions. [ABSTRACT FROM AUTHOR]

Abstract: Growth of hydrogenated amorphous silicon in a doping inversed silicon heterojunction solar cell (n-a-Si:H/i-a-Si:H/p-c-Si) interface was investigated by High Resolution Transmission Electron Microscopy (HR-TEM), Spectroscopic Ellipsometry (SE), Fourier Transform Infrared Attenuated Total Reflection spectroscopy (FTIR-ATR) and current–voltage (I–V) measurements. Effective Medium Approximation (EMA) to the SE was used to describe breakage of epi-Si and evolution of mixture of microcrystalline and amorphous phases. Fabricated silicon heterojunction solar cells were characterized by dark and light I–V measurements at Standard Test Conditions. By improving the cleaning and deposition conditions, solar cells with 9.2% efficiency over 72cm2 total active area were obtained on p-type c-Si wafers. [Copyright &y& Elsevier]