Titanium Dioxide (TiO2) Selective Contact for Solar Cells

What is it about?

Our work at Stanford University describes the design and fabrication of a novel metal-insulator-semiconductor (MIS) selective contact to c-Si solar cells. I. The 2 μm-thick Si cell with this TiO2 MIS contact achieved a Voc of 645 mV, higher than published c-Si cells with similar thickness. II. Demonstration on the open circuit voltage (Voc) and efficiency enhancement by TiO2 MIS contacts in ultra-thin-film c-Si cells. Key designs in this TiO2 MIS c-Si cell are: I. TiO2/n-Si has the ideal band alignment for the hole-blocking contact. a. TiO2 has a large valance band (VB) offset and provides good passivation to n-Si, which can significantly reduce the recombination loss of holes. b. TiO2 can unpin the Fermi level at the Si surface and eliminate the energy barrier for electron transport, resulting in high conductance for electrons. II. TiO2 is selectively deposited at the metal contact area only. The rest surface area of Si is covered by SiO2, which can provide even better passivation and further reduce recombination loss at Si surfaces.

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Why is it important?

One of the challenges for ultra-thin-film c-Si solar cells has been to reduce the recombination loss at Si surfaces and metal contacts, and to realize a high open circuit voltage. We target this fundamental challenge, systemically study the recombination loss mechanisms in ultra-thin-film c-Si cells, and present the key design principles to achieve high efficiencies.