Energy Migration in Organic Solar Concentrators with a Molecularly Insulated Perylene Diimide

Abstract

Maintaining high incident light absorption while minimizing luminescence reabsorption is a key challenge for organic luminescent solar concentrators (LSCs). Energy migration and trapping using light-harvesting donors and a low-energy highly emitting acceptor is one strategy to reduce the reabsorption issue. However, concentration quenching and the potential formation of quenching aggregates is a limiting factor in realizing efficient devices. We describe the synthesis of a novel molecularly insulated perylene diimide that can resist luminescence quenching at concentrations in excess of 50 mM. Photophysical measurements show the insulated perylene diimide has an excitation energy migration diffusion length of 230 ± 10 Å at 60 mM in poly(methyl methacrylate). LSC devices using a mixture of the insulated perylene diimide light absorber and perylene red (LR305) as the low-energy trap emitter exhibit reduced reabsorption and a better current output than LR305 only devices. The results demonstrate that appropriately designed organic molecule dyes can potentially meet the stringent requirements required for efficient LSCs. S tationary light concentration without external cooling can be realized using luminescent solar concentrators (LSCs), making these devices attractive for building integrated photovoltaic devices. A typical LSC consists of large sheets of plastic or glass containing luminescent molecules that absorb the solar spectrum and then re-emit the absorbed energy into a waveguide mode that directs the luminescence to the thin edges of the concentrator. Edge-mounted solar cells can then harvest the concentrated luminescence for photoelectric conversion. Reabsorption of the emitted light in the waveguide limits the achievable light concentration contributing to parasitic losses such as re-emission into the escape cone or nonunity fluorescence quantum efficiency due to competing nonradiative processes. Separation of both the energy of the peak maxima of absorption and emission (the Stokes shift) and tail absorption of the chromophores in an LSC is crucial in reducing reabsorption. 1,2 Organic solar concentrators that use diluted organic chromophores in inert host matrices are lagging behind their inorganic counterparts due to their small Stokes shifts. 3 A key advantage of organic chromophores over inorganic materials is their solubility in inexpensive host matrices or waveguides, such as poly(methyl methacrylate) (PMMA) or glass, without any complicated processing and the ability to fine-tune their properties by simple molecular engineering approaches. This is particularly important for thin-film LSCs where the concentration required to achieve total light absorption over the wavelength range of the chromophore can be high ( Figure 1).Modification of dyes to achieve a large Stokes shift has achieved only limited success for LSC applications. In some cases, increasing the Stokes shift of the dye has led to a decreased quantum yield and there often remains the long tail absorption of the dye. 4 Energy transfer ...

Luminescent Solar Concentrators Based on Energy Transfer from an Aggregation-Induced Emitter Conjugated Polymer

“…To experimentally investigate the effect of In the mixed samples, the PDI-Sil emission intensity increases steadily with concentration and is accompanied by a decrease in the p-O-TPE emission, which suggests the occurrence of FRET (of increasing efficiency) between the two lumophores. 26,49,50 In addition, the characteristic excitation features of p-O-TPE are present in excitation spectra ( Figure S3, ESI) selectively detected for PDI-Sil emission (λem = 650 nm), which provides further evidence for the occurrence of FRET. However, PDI-Sil itself can also be moderately excited at 370 nm as the tail of its absorption band lies in this region ( Figure 2).…”

Aggregation-induced emission-mediated spectral downconversion in luminescent solar concentrators

“…An emissive donor of significantly high concentration within the LSC matrix absorbs light and transfers its energy non-radiatively via Förster mechanism to an acceptor that has a comparatively lower concentration in the film. [9][10][11][12] The acceptor then emits at longer wavelengths compared to the incident light. By optimizing the concentration and ratio of donor and acceptor chromophores in the LSC, reabsorption from the acceptor can be mitigated while maintaining efficient light-harvesting.…”

“…By optimizing the concentration and ratio of donor and acceptor chromophores in the LSC, reabsorption from the acceptor can be mitigated while maintaining efficient light-harvesting. [9][10][11]13 Using this energy migration and trapping approach for LSCs provides broad tunability in the emission wavelengths and absorption bandwidth of LSCs. Our group recently reported the use of FRET donor chromophores that showed high φPL at high concentration in poly(methyl methacrylate) (PMMA).…”

Star-shaped fluorene–BODIPY oligomers: versatile donor–acceptor systems for luminescent solar concentrators

“…18,19 For organic molecules where the Stokes shift may be considered intrinsic, the donor-acceptor strategy is prevalent, and many LSCs using donor-acceptor systems based on Förster resonance energy transfer (FRET) have been reported. [20][21][22][23][24] FRET permits efficient radiationless energy transfer between donors and acceptors, but only if the coupled molecules are within E5 nm of each other. 16,[25][26][27] This degree of proximity in molecules containing large p-systems often leads to aggregation and decreased photoluminescence quantum efficiencies (PLQEs), [28][29][30][31][32] which hinder LSC performance.…”