Silicon solar cells are approaching their efficiency limit of 29% under the standard solar spectrum. In order to surpass this limit, a device is required that better manages the energy in each incoming energy packet (photon). One approach to this end is to split the energy of higher energy photons in two, such that two electron-hole pairs can be generated by one photon. This strategy has an upper limit of 45.9%. Organic Multiple Exciton Generation (OMEG) is executed by a photophysical process called singlet fission. A spin-0 (singlet) exciton is generated by a photon, and it decays into two spin-1 triplet excitons in a spin-conserving process. This talk will detail our progress towards developing OMEG augmented silicon solar cells (OMEGA-Si).
Layers of organic molecules are capable of generating multiple excitons per absorbed photon though a process known as singlet fission. As such, this process could be employed to fabricate a solar cell which circumvents the efficiency limits imposed by a single threshold design. Leveraging experience with silicon solar cells, the OMEGA Si project is developing a device that combines the maturity and high efficiency of crystalline silicon with the exciton multiplication afforded by singlet fission. This talk will communicate progress of the project including experiments to elucidate exciton and carrier transfer between the singlet fission layer and the underlying silicon solar cell.
Metal nanoparticles are known for their unique optical properties due to surface plasmon excitations. The far field and
near field effects from these metal particles have been captured to enhance efficiency of thin film solar cells by way of
light trapping. Our group has extensively studied the different design parameters for a plasmon enhanced solar cell like
effect of metal size/shape, location, effect of dielectric layer thickness and also the effect of plasmons on the electrical
properties like passivation of cells. Whilst identifying and minimising parasitic absorption losses in these metal particles
are important and is attracting lot of attention, we choose to look at a more interesting issue of ageing effects. Plasmonics
at the moment promises efficiency enhancements exceeding 30% including associated losses in metals. However as is
needed for solar cells, the technologies incorporated have to stand the test of time. In this work we look at the age effects
on the plasmon performance by analysing our cells over time. Our preliminary results show that plasmons supported by
silver metal nanoparticles can degrade by upto 10% with time. Metal nanoparticles when exposed to air can get tarnished
easily causing degradation of the plasmonic properties. This will result in weakening of the scattering and reduce light
trapping effects. We also look at ways of minimizing the ageing losses by overcoating. MgF2 is used as the dielectric
film to overcoat metal nanoparticles preventing degradation and also to isolate MNP layer from the back surface
reflector of cells. Our results show that such a rear scheme brings an additional current enhancement over interested
wavelength region improving over time.
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