Characterization of the SnO_{2}/p Contact Resistance and SnO_{2} Properties in Operating a-Si:H p-i-n Solar Cells


Abstract: A method is presented to characterize the TCO/p contact and the TCO sheet resistance in a-Si TCO/p-i-n superstrate devices. It is extremely useful for understanding resistance losses in modulus and diagnosing how plasma processing influences the TCO layers. Analysis of 4-terminal dark J-V measurements as a function of temperature on devices with varying TCO geometry yields the TCO/p contact resistance R_{TCO/p}, its activation energy E_{a} or barrier height, and the TCO sheet resistance R_{SH} in an integrated device structure. The method is applied to devices fabricated on different brands of commercial SnO_{2} substrates with different p-layers. Important new results are found. E_{a} for the SnO_{2}/p contact resistance are about 40-50 meV which is < 2kT, and therefore not a rectifying barrier. R_{SH} in one brand of SnO_{2} has a benefical decrease of 60% after a-Si deposition while another brand is unaffected. The impact of R_{SH} or R_{TCO} losses on the FF (fill factor) are determined.

Keywords: TCO/p contact resistance, SnO_{2} properties, a-Si:H p-i-n solar cells.

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