Photochemical upconversion is applied to a hydrogenated amorphous silicon solar cell in the presence of a back-scattering layer. A custom-synthesized porphyrin was utilized as the sensitizer species, with rubrene as the emitter. Under a bias of 24 suns, a peak external quantum efficiency (EQE) enhancement of ∼2% was observed at a wavelength of 720nm. Without the scattering layer, the EQE enhancement was half this value, indicating that the effect of the back-scatterer is to double the efficacy of the upconverting device. The results represent an upconversion figure of merit of 3.5×10 -4mAcm -2sun -2, which is the highest reported to date.