Singlet
fission in tetracene generates two triplet excitons per
absorbed photon. If these triplet excitons can be effectively transferred
into silicon (Si), then additional photocurrent can be generated from
photons above the bandgap of Si. This could alleviate the thermalization
loss and increase the efficiency of conventional Si solar cells. Here,
we show that a change in the polymorphism of tetracene deposited on
Si due to air exposure facilitates triplet transfer from tetracene
into Si. Magnetic field-dependent photocurrent measurements confirm
that triplet excitons contribute to the photocurrent. The decay of
tetracene delayed photoluminescence was used to determine a transfer
efficiency of ∼36% into Si. Our study suggests that control
over the morphology of tetracene during the deposition will be of
great importance to boost the triplet transfer yield further.
Ytterbium-doped lead halide perovskite (Yb3+:CsPbX3 with x = Cl or Cl/Br) nanocrystals and thin films have shown surprisingly efficient downconversion by quantum cutting with PLQYs up to 193%.
Carrier
multiplication (CM) generates multiple electron–hole
pairs in a semiconductor from a single absorbed photon with energy
exceeding twice the band gap. Thus, CM provides a promising way to
circumvent the Shockley–Queisser limit of solar cells. The
ideal material for CM should have significant overlap with the solar
spectrum and should be able to fully utilize the excess energy above
the band gap for additional charge carrier generation. We report efficient
CM in mixed Sn/Pb halide perovskites (band gap of 1.28 eV) with onset
just above twice the band gap. The CM rate outcompetes the carrier
cooling process leading to efficient CM with a quantum yield of 2
for photoexcitation at 2.8 times the band gap. Such efficient CM characteristics
add to the many advantageous properties of mixed Sn/Pb metal halide
perovskites for photovoltaic applications.
Silicon solar cells are operating close to the theoretical maximum efficiency limit. To increase their efficiency beyond this limit, it is necessary to decrease energy losses occurring for high-energy photons. A sensitizing layer of singlet-fission material can in principle double the current generated by high-energy photons, and significantly reduce energy losses from high-energy photons within the solar cell. Here, we construct a model of such a solar cell, using Si(111) surfaces and tetracene. To increase the energy transfer between the two layers, a series of tetracene derivatives was synthesized, and the molecules were covalently attached onto the silicon surface as a seed layer. Using X-ray diffraction, a shift in crystal structure and ordering of the tetracene close to the seed layer can be observed. Unfortunately, the effect on the energy transfer was limited, showing a need for further investigations into the effect of the seed layer.
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