Enhancing the near-infrared spectral response of silicon optoelectronic devices via up-conversion

A silicon-based optoclectronic 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 (NaY0.8 : Er-0.2(3+)) phosphors are the optically yttrium fluoride active centers responsible for the UC luminescence. The unoptimized device is demonstrated to respond effectively to wavelengths (A) 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 x 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 x 10(-2) cm(2)/W), while further potential device improvements indicate that an EQE of 14.0% (5.8 x 10(-2) cm(2)/W) could be realistically achieved.