Relaxation processes in silicon heterojunction solar cells probed via noise spectroscopy

Abstract

We have employed state-of-the-art cross-correlation noise spectroscopy (CCNS) to study carrier dynamics in silicon heterojunction solar cells (SHJ SCs). These cells were composed of a light absorbing n-doped monocrystalline silicon wafer contacted by passivating layers of i-a-Si:H and doped a-Si:H selective contact layers. Using CCNS, we are able to resolve and characterize four separate noise contributions: (1) shot noise with Fano factor close to unity due to holes tunneling through the np-junction, (2) a 1/f term connected to local potential fluctuations of charges trapped in a-Si:H defects, (3) generation-recombination noise with a time constant between 30 and 50 μs and attributed to recombination of holes at the interface between the ITO and n-a-Si:H window layer, and (4) a low-frequency generation-recombination term observed below 100 K which we assign to thermal emission over the ITO/ni-a-Si:H interface barrier. These results not only indicate that CCNS is capable of reveling otherwise undetectable relaxation process in SHJ SCs and other multi-layer devices, but also that the technique has a spatial selectivity allowing for the identification of the layer or interface where these processes are taking place.

Electrically Detected Magnetic Resonance on a Chip (EDMRoC) for Analysis of Thin-Film Silicon Photovoltaics

“…As the ∆I d /I d obtained with the EDMRoC is a factor of 30 less than that obtained using the Elexsys spectrometer, the noise in the EDMRoC measurements was therefore approximately a factor of 10 greater than that obtained using the Elexsys spectrometer. This increase may be attributed to the additional shot noise present in the solar cell when it was placed on the EDMRoC, and was further supported by the decrease in the SNR observed in the conventional resonator ( SNR T=302 K SNR T=336 K ≈ 12) with respect to the increased temperature [52,63]. It was observed when performing the EDMRoC measurements using an EPRoC with thermal dissipation via direct contact with the copper substrate contained within the PCB and an external homebuilt TIA that the SNR was increased by a factor of two, demonstrating the potential improvements to the noise floor by decreasing the temperature of the VCO array (data not shown).…”