Energy Upconversion via Triplet Fusion in Super Yellow PPV Films Doped with Palladium Tetraphenyltetrabenzoporphyrin: a Comprehensive Investigation of Exciton Dynamics

Abstract

One of the key issues concerning the development of efficient polymer solar cell technology is the lack of viable materials which absorb in the near‐infrared (NIR) region. This could be resolved by up‐converting energy from the NIR into visible using triplet fusion (TF) with an additional layer that is fabricated separately from the solar cell and deposited on top. Theoretically a maximum upconversion (UC) via TF efficiency of 50% could be obtained. Here, it is demonstrated that in a film of commercially available poly(para‐phenylene vinylene) copolymer “super yellow” (SY) doped with 4% palladium(meso‐tetraphenyl‐tetrabenzoporphyrin) (PdTPBP) sensitizer, an UC efficiency of 6% can be achieved. By using femtosecond and nanosecond spectroscopies it is shown that the main UC efficiency loss mechanism is due to triplet quenching in PdTPBP aggregates. The PdTPBP intersystem crossing rate constant is determined to be 1.8 × 1011 s−1 and the triplet energy transfer rate constant from PdTPBP to SY to be 109 s−1. Quenching in PdTPBP aggregates can account for a triplet concentration loss in the range of 76‐99%. As such, preventing sensitizer aggregation in NIR‐to‐visible upconverting films is crucial and may lead to substantial increase of UC efficiencies in films.

Indirect consequences of exciplex states on the phosphorescence lifetime of phenazine-based 1,2,3-triazole luminescent probes

“…The slope of (1.75 ± 0.06) corresponding to the band at 464 nm approaches the value of 2, which strongly suggests TTA mechanism at a regime of relatively low laser intensities. 17 For the band at 608 nm the growing rate (1.13 ± 0.02) reconfirms what was expected for phosphorescent recombination.…”

Photochemical upconversion: present status and prospects for its application to solar energy conversion

“…Regarding emitter species, most studies have focussed on PAHs, with BODIPY-and conjugated polymer-based emitters being notable exceptions. 16,32 Comprehensive review articles regarding the plethora of molecular species employed in TTA systems include the works of Singh-Rachford et al 16 and Zhao et al 17 .…”

Photochemical upconversion of light for renewable energy and more

“…Indeed, some researchers have found that aggregation of sensitizers caused up to 97 % loss of triplet states. 31 However, as will be shown below, such a strategy should be approached with caution.…”