Origin of the Tunable Carrier Selectivity of Atomic-Layer-Deposited TiOx Nanolayers in Crystalline Silicon Colar Cells
- Fraunhofer Institute for Solar Energy Systems ISE; National Institute of Advanced Industrial Science and Technology
- Fraunhofer Institute for Solar Energy Systems ISE
- National Renewable Energy Laboratory (NREL), Golden, CO (United States)
- University of Oxford
Titanium oxide (TiOx) nanolayers grown by atomic layer deposition are investigated with respect to their application as carrier selective contacts for crystalline silicon (c-Si) solar cells. Although TiOx is known to act as an electron contact, in this work the selectivity of TiOx layers is found to be widely tunable from electron to hole selective depending on deposition conditions, post-deposition treatments, and work function of the metal electrode used. Using TiOx and an intrinsic hydrogenated amorphous silicon buffer layer, solar cell test structure exhibiting open-circuit voltages (Voc) as high as 720 and 650 mV are shown for electron and hole selective contacts, respectively. Surface photovoltage and capacitance-voltage measurements reveal that carrier selectivity is correlated with the amount of c-Si band bending induced by TiOx, which are governed not only by the effective work function difference at the Si/TiOx interface, but also by the negative fixed charge present in the TiOx layer. This new finding is in contrast to the previous model for carrier transport where selectivity is determined only by the asymmetric band offsets at the Si/contact interface. It highlights the influence of induced band bending to produce carrier depletion/inversion conditions, and the importance of its selectivity effect in a c-Si absorber.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE)
- DOE Contract Number:
- AC36-08GO28308
- OSTI ID:
- 1603927
- Report Number(s):
- NREL/JA-5900-76276
- Journal Information:
- Solar Energy Materials and Solar Cells, Vol. 209
- Country of Publication:
- United States
- Language:
- English
Similar Records
Evaluation of transition metal oxide as carrier-selective contacts for silicon heterojunction solar cells
Amorphous Silicon Carbide Passivating Layers to Enable Higher Processing Temperature in Crystalline Silicon Heterojunction Solar Cells