Whispering Gallery Mode Assisted Enhancement in the Power Conversion Efficiency of DSSC and QDSSC Devices Using TiO2 Microsphere Photoanodes

Mesoporous TiO2 nanoparticles are excellent photoanodes for sensitized solar cells (SSC). However, a significant loss in the photoconversion efficiency (PCE) occurs due to the inefficient light absorption. Large Mie scattering from mesoporous micron-sized spheres could be used to enhance the absorption and hence the PCE. Here, we show that a composite comprising a TiO2 mesoporous microsphere with smooth surface (S mu S-TiO2) exhibiting whispering gallery modes (WGM) and a commercial TiO2 mesoporous nanoparticle (Degussa P25) with an optimum ratio (80:20 wt %) shows significant enhancement in PCE of DSSC and QDSSC devices. S mu S-TiO2 exhibits strong WGM as evidenced from the photoluminescence studies carried out using a laser with an excitation wavelength lambda(exc) = 325 nm. These microspheres sensitized with N719 dye or CdSe/CuInS2 QDs are shown to exhibit emission characteristics strongly coupled to WGM resulting in an enhanced PCE in SSC. Increases in PCE of similar to 24% in DSSC devices and 80-95% in QDSSC devices of 0.25 cm(2) area are demonstrated. Thus, TiO2 composite exhibiting WGM can be used as a generic photoanode to achieve maximum PCE for Gratzel type sensitized solar cells. This study suggests special class of solar cells called "whisperonic solar cells".