Tunneling and recombination processes in silicon heterojunction solar cells (SHJSCs) observed via spatially selective noise spectroscopy*

We have employed state-of-the-art cross-correlation noise spectroscopy (CCNS) to study carrier dynamics in silicon heterojunction solar cells (SHJ SCs) 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 during operation.  First, we observe shot noise with Fano factor close to unity due to holes tunneling through the np-junction.  Second, a 1/f term connected to local potential fluctuations of charges trapped in a-Si:H defects.  Third, a generation-recombination noise with a time constant between 30-50 μs and attributed to recombination of holes at the interface between the ITO and n-a-Si:H window layer.  Finally, we observe 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 revealing 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.