Collaborative effect of plasmon-induced resonance energy and electron transfer on the interfacial electron injection dynamics of dye-sensitized solar cell

It has been widely recognized that plasmonic metal nanoparticles (MNPs) can enhance the power convention efficiency (PCE) of dye-sensitized solar cells (DSSCs). This enhancement is ascribed to the combined effects of plasmon decay, scattering, near-field enhancement, and exciting charge carriers in semiconductors through plasmon-induced resonance energy transfer (PIRET) and hot electron injection (HEI). PIRET and HEI processes appeared between MNPs, and semiconductors have been intensively investigated; however, it is not clear how the collaborative effect of PIRET and photon-induced direct and indirect electron transfer (PICT) occurred between plasmonic metals and dyes, and the interference of different charge separation channels (CSCs) starting from PIRET and PICT affects the PCE of DSSCs. This work aims to address these issues. We apply a model Hamiltonian method, which obviously includes both PIRET and PICT processes from Au MNP to dye molecules and incorporates the dye's electron-phonon interaction, to investigate the carrier dynamics. It is found that PIRET deforms the wavepacket dynamics of the molecular excited state and results in ten-fold enhancement of dye absorption. MNPs augment light absorption and increase the electron density in empty molecular orbitals of the dye molecule. Consequently, this enhances the interfacial charge separation. Furthermore, we observed the interference behavior of two CSCs and gave a full-scale insight into the correlation between the constructive/destructive interference and the electronic-state properties as well as carrier-phonon interactions. This work provides a theoretical guidance to optimize DSSCs.

Three-in-one approach towards efficient organic dye-sensitized solar cells: aggregation suppression, panchromatic absorption and resonance energy transfer

In the present study, protoporphyrin IX (PPIX) and squarine (SQ2) have been used in a co-sensitized dye-sensitized solar cell (DSSC) to apply their high absorption coefficients in the visible and NIR region of the solar spectrum and to probe the possibility of Förster resonance energy transfer (FRET) between the two dyes. FRET from the donor PPIX to acceptor SQ2 was observed from detailed investigation of the excited-state photophysics of the dye mixture, using time-resolved fluorescence decay measurements. The electron transfer time scales from the dyes to TiO2 have also been characterized for each dye. The current-voltage (I-V) characteristics and the wavelength-dependent photocurrent measurements of the co-sensitized DSSCs reveal that FRET between the two dyes increase the photocurrent as well as the efficiency of the device. From the absorption spectra of the co-sensitized photoanodes, PPIX was observed to be efficiently acting as a co-adsorbent and to reduce the dye aggregation problem of SQ2. It has further been proven by a comparison of the device performance with a chenodeoxycholic acid (CDCA) added to a SQ2-sensitized DSSC. Apart from increasing the absorption window, the FRET-induced enhanced photocurrent and the anti-aggregating behavior of PPIX towards SQ2 are crucial points that improve the performance of the co-sensitized DSSC.