Whispering Gallery Mode Assisted Enhancement in the Power Conversion Efficiency of DSSC and QDSSC Devices Using TiO<inf>2</inf> 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 (SμS-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. SμS-TiO2 exhibits strong WGM as evidenced from the photoluminescence studies carried out using a laser with an excitation wavelength λexc = 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 ∼24% in DSSC devices and 80-95% in QDSSC devices of 0.25 cm2 area are demonstrated. Thus, TiO2 composite exhibiting WGM can be used as a generic photoanode to achieve maximum PCE for Grätzel type sensitized solar cells. This study suggests special class of solar cells called "whisperonic solar cells".