title: Composition-graded nanowire solar cells fabricated in a single process for spectrum-splitting photovoltaic systems.
abstract: Nanomaterials such as semiconductor nanowires have unique features that could enable novel optoelectronic applications such as novel solar cells. This paper aims to demonstrate one such recently proposed concept: Monolithically Integrated Laterally Arrayed Multiple Band gap (MILAMB) solar cells for spectrum-splitting photovoltaic systems. Two cells with different band gaps were fabricated simultaneously in the same process on a single substrate using spatially composition-graded CdSSe alloy nanowires grown by the Dual-Gradient Method in a chemical vapor deposition system. CdSSe nanowire ensemble devices tested under 1 sun AM1.5G illumination achieved open-circuit voltages up to 307 and 173 mV and short-circuit current densities as high as 0.091 and 0.974 mA/cm(2) for the CdS- and CdSe-rich cells, respectively. The open-circuit voltages were roughly three times those of similar CdSSe film cells fabricated for comparison due to the superior optical quality of the nanowires. I-V measurements were also performed using optical filters to simulate spectrum-splitting. The open-circuit voltages and fill factors of the CdS-rich subcells were uniformly larger than the corresponding CdSe-rich cells for similar photon flux, as expected. This suggests that if all wires can be contacted, the wide-gap cell is expected to have greater output power than the narrow-gap cell, which is the key to achieving high efficiencies with spectrum-splitting. This paper thus provides the first proof-of-concept demonstration of simultaneous fabrication of MILAMB solar cells. This approach to solar cell fabrication using single-crystal nanowires for spectrum-splitting photovoltaics could provide a future low-cost high-efficiency alternative to the conventional high-cost high-efficiency tandem cells.
authors.affiliation: ASU Nanophotonics Lab, Arizona State University , Tempe, Arizona 85287, United States.
authors.forename: Derek
authors.initials: D
authors.lastname: Caselli
authors.forename: Zhicheng
authors.initials: Z
authors.lastname: Liu
authors.forename: David
authors.initials: D
authors.lastname: Shelhammer
authors.forename: Cun-Zheng
authors.initials: CZ
authors.lastname: Ning
keywords: Nanowires; composition-graded; semiconductor alloys; solar cells; spectrum-splitting