Photocurrent Enhanced by Singlet Fission in a Dye-Sensitized Solar Cell

Abstract

Investigations of singlet fission have accelerated recently because of its potential utility in solar photoconversion, although only a few reports definitively identify the role of singlet fission in a complete solar cell. Evidence of the influence of singlet fission in a dye-sensitized solar cell using 1,3-diphenylisobenzofuran (DPIBF, 1) as the sensitizer is reported here. Self-assembly of the blue-absorbing 1 with co-adsorbed oxidation products on mesoporous TiO2 yields a cell with a peak internal quantum efficiency of ∼70% and a power conversion efficiency of ∼1.1%. Introducing a ZrO2 spacer layer of thickness varying from 2 to 20 Å modulates the short-circuit photocurrent such that it is initially reduced as thickness increases but 1 with 10-15 Å of added ZrO2. This rise can be explained as being due to a reduced rate of injection of electrons from the S1 state of 1 such that singlet fission, known to occur with a 30 ps time constant in polycrystalline films, has the opportunity to proceed efficiently and produce two T1 states per absorbed photon that can subsequently inject electrons into TiO2. Transient spectroscopy and kinetic simulations confirm this novel mode of dye-sensitized solar cell operation and its potential utility for enhanced solar photoconversion.

Theoretical Studies of Singlet Fission: Searching for Materials and Exploring Mechanisms

“…In a dye‐sensitized solar cell, SF is a competitive process only when a spacer layer slows down electron injection of singlet excitons . This finding motivated Strong and Eaves to simulate the aggregation of tetracene on a model surface and investigate the dependence of the packing geometry of the aggregate on the polarity of the surface .…”

Dynamics of singlet fission and electron injection in self-assembled acene monolayers on titanium dioxide

“…A later study utilizing 1,3-diphenylisobenzofuran (DPIBF) and TiO 2 focused on a fundamental examination of the interplay between SF and charge injection dynamics. 46 A small increase in photocurrent was observed upon reducing the electron injection rate with a zirconia barrier, which allowed SF to produce multiple triplet excitons that could dissociate. However, the intermolecular geometries appropriate for SF with DPIBF are restrictive, 47 which most likely reduced the photocurrent enhancement.…”

Polymorphism influences singlet fission rates in tetracene thin films

“…While much theoretical 6 – 14 and experimental 15 – 21 work has focused on the mechanism of SF, it has only been utilized in a few PV device moieties. 22 – 25 From the limited number of applications, it is clear that taking full advantage of SF requires a more complete understanding of the mechanism and a wider array of systems supporting efficient SF.…”