Simplifying silicon solar cells with passivating/carrier-selective materials.

What is it about?

An efficient silicon solar cell design must compromise between two requirements: 1) defect passivation with insulating materials (to maximize photovoltage), and 2) selective extraction of positive/negative carriers via conductive materials (to maximize photocurrent). This calls for multiple materials deposited by different methods (usually at high temperatures) and with dissimilar area coverage. Hence, why not use a single semi-insulating material which can both passivate while selectively conduct charge? Moreover, what if this material is deposited by low-temperature simple processes? This paper discusses the application of thermally-evaporated transition metal oxides (V2O5, MoO3) to crystalline silicon solar cells, inquiring in the origin of their dual-functionality as passivating/hole-selective materials.

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Why is it important?

Our findings suggest that passivation of the silicon surface occurs by a SiOx ultra-thin layer which forms by spontaneous chemical reaction between silicon and the metal oxide. Additionally, this layer is poor in oxygen and allows to extract carriers (holes), performing a passivating/conducting function. Given that transition metal oxides can be deposited by low-temperature and/or solution-based processes, this offers the possibility of simplifying solar cell fabrication and reducing costs.

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