Executive Summary :
Objective: Synthesizing the chromophores having the specific features including strong interchromophore coupling, high triplet yield, strong visible absorption, rigid and high conjugation, biradicaloids in nature, efficient charge separation and long stability in light, to unambiguously show the singlet fission processes. Steady state photophysical properties of the chromophores will be investigated in solution and film state. As the strong evidence of the occurrence of singlet fission process is the existence of higher triplet quantum yield of chromophores, excited state dynamics including bleach, singlet and triplet state, stimulated emission, radical formation and decay time constants of the chromophores in thin film state will be investigated with femtosecond pump-probe and nano second laser flash photolysis spectrophotometer. Temperature and excitation energy dependent transient absorption spectra will be measured to explore the deactivation pathways of non-radiative transition, singlet-singlet and triplet-triplet annihilation, excimer-trapping. Ideal chromophores will be applied in devices for hybrid bulk hetero junction and the solar cell efficiency and IPCE can be measured.
Summary: Singlet exciton fission (SF), a photophysical process, has gained interest recently towards solar cell application as it converts high energy photons into two excitons. However the basic concept of SF mechanism is yet to be solved. As SF could minimize the losses caused by relaxation, SF sensitizer can be used as potential candidate for devices in solar cell. This project starts with identifying the molecules possessing specific features of high triplet yield, strong visible absorption, rigid and high conjugation, biradicaloids in nature, efficient charge separation, strong interchromophore coupling and long stability in light. Mainly excited state dynamics of specific chromophores will be investigated to evaluate the underlying mechanism of SF by measuring the singlet and triplet state absorption spectra, lifetime and quantum yields with femtosecond pump probe and nanosecond laser flash photolysis spectrophotometer. Finally, the design guidelines for an ideal molecule will be developed and photovoltaic cell performance will be studied.