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
_0.8
F
₄
: 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/cm
²
(EQE = 1.4 times 10
^-2
cm
²
/W). An analysis of the optical losses reveals that the luminescence quantum efficiency (LQE) of the device is 16.7% at 2.4 W/cm
²
of 1523-nm excitation (LQE = 7.0 times 10
^-2
cm
²
/W), while further potential device improvements indicate that an EQE of 14.0% (5.8 times 10
^-2
cm
²
/W) could be realistically achieved.