Avi Shalav

Application of NaYF4:Er3+ up-converting phosphors for enhanced near-infrared silicon solar cell response

Erbium-doped sodium yttrium fluoride (NaYF4:Er3+) up-conversion phosphors were attached to the rear of a bifacial silicon solar cell to enhance its reponsivity in the near-infrared. The incident wavelength and light intensity were varied and the resulting short circuit current of the solar cell was measured. A close match between the spectral features of the external quantum efficiency and the phosphor absorption is consistent with the energy transfer up-conversion process. The peak external quantum efficiency of the silicon solar cell was measured to be (2.5±0.2)% under 5.1 mW laser excitation at 1523 nm, corresponding to an internal quantum efficiency of 3.8%.

Enhancing the Near-Infrared Spectral Response of Silicon Optoelectronic Devices via Up-Conversion

A silicon-based optoelectronic device that exhibits an enhanced response to subbandgap light is described. The device structure consists of a bifacial silicon solar cell with an up- converting (UC) layer attached to the rear. Erbium-doped sodium yttrium fluoride (NaY_0.8F₄ : Er_0.2 ³⁺) phosphors are the optically active centers responsible for the UC luminescence. The unoptimized device is demonstrated to respond effectively to wavelengths (lambda) in the range of 1480-1580 nm with an external quantum efficiency (EQE) of 3.4% occurring at 1523 nm at an illumination intensity of 2.4 W/cm² (EQE = 1.4 times 10^-2 cm²/W). An analysis of the optical losses reveals that the luminescence quantum efficiency (LQE) of the device is 16.7% at 2.4 W/cm² of 1523-nm excitation (LQE = 7.0 times 10^-2 cm²/W), while further potential device improvements indicate that an EQE of 14.0% (5.8 times 10^-2 cm²/W) could be realistically achieved.

Improvements of an up-conversion NaYF/sub 4/:Er/sup 3+/ phosphor/silicon solar cell system for an enhanced response in the near-infrared

This study investigates the performance of up-converting rare-earth phosphors doped with different trivalent erbium (Er/sup 3+/) concentrations: 2%, 20%, 50%, 100%, and with the addition of 20% ytterbium (Yb). The dominant up-conversion (UC) mechanisms within these phosphors are discussed and examined using photoluminescence and the spectral response from a bifacial silicon solar cell. The most efficient phosphor examined had 20% Er doping and gave a maximum external quantum efficiency close to 3.4% with 6 mW 1523 nm laser excitation. The subsequent system internal quantum efficiency (accounting for reflection losses within the cell) is calculated to be over 5.7%.

Two Colour Excitation Up-Conversion Efficiency Enhancement for a Silicon Photovoltaic Device using Er3+-Doped Phosphors

This paper summarises the dominant up-conversion (UC) mechanisms of single wavelength illumination of Er3+ doped phosphors. The excitation spectra for three separate UC mechanisms are shown not to overlap with the absorption band of the higher level(s) (2-step) of the Er3+ ions. Higher UC efficiencies are more probable using at least two separate light energies directly pumping the required levels of the Er3+ ions via ground state absorption/excited state absorption (GSA/ESA) mechanisms. The dominant up-conversion mechanism under two-colour excitation using Er3+ doped phosphors is investigated and the spectral robustness of a photovoltaic-upconversion (PV-UC) device is analysed. The resulting dependence of the excited intermediate level on incident pump power is also discussed