ERC Researchers Develop Silicon Solar Cells that Produce World-Record Open-Circuit Voltages
Researchers at the NSF-funded Engineering Research Center (ERC) for Quantum Energy and Sustainable Solar Technologies (QESST), which is headquartered at Arizona State University, have developed a process that forms new layers in a silicon solar device, thereby enabling achievement of an open-circuit voltage of 753 mV [Herasimenka et al., 2013a].
The new process permits thinner wafers with higher efficiency and achieves the dual goal of reducing cell cost and increasing module power output. A decade ago the practical limit on cell open-circuit voltage was considered to be720mV, with the voltage of a typical commercial solar cell under 650 mV. The recent high open-circuit voltage exceeding 750 mV surpasses the previous limit to increasing cell efficiency, represents a world-record for a silicon solar cell under one sun illumination, and demonstrates that high-efficiency cells can be fabricated on thin substrates.
A challenge in manufacturing silicon solar cells is to simultaneously reduce the cost and increase the cell efficiency. For solar cells with passivated surfaces, the efficiency of the solar cell increases as the cell thickness is reduced. In contrast, cells without these surfaces exhibit decreased cell efficiency with cell thickness. By using thinner cells, less material is consumed and material supply costs are lower.
Using commercially grown (Czochralski) silicon from a vendor, the ERC researchers achieved a carrier lifetime of 15 ms [Herasimenka et al., 2013b], the highest reported on wafers used for solar manufacture. High lifetimes (e.g., see figure) demonstrate that low levels of defects are possible in commercial production. From lifetime measurements it was determined that voltages exceeding 760 mV are possible and that crystalline silicon will be able to achieve power conversion efficiencies of 26%.