Luminescent solar concentrators have received renewed interest because they can harvest solar radiation without the need for expensive tacking systems. In this work, highly efficient luminescent waveguiding photovoltaic devices exhibiting mechanical flexibility and solar concentration ability have been prepared by integrating Si solar cells with soft polydimethylsiloxane (PDMS) waveguides. We observed that segregated dyes in the PDMS waveguides induce strong scattering effects in the long-wavelength range. The scattered photons were transported effectively to the solar cells, leading to high power conversion efficiencies (PCEs). A single module exhibited a remarkable power conversion efficiency of 4.62±0.02%. After stacking two waveguides, we achieved PCEs as high as 5.23±0.01%, with a projected PCE approaching 12%.