Highly efficient large-area colourless luminescent solar concentrators using heavy-metal-free colloidal quantum dots

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1 Highly efficient large-area colourless luminescent solar concentrators using heavy-metal-free colloidal quantum dots Francesco Meinardi*, Hunter Mc Daniel, Francesco Carulli, Annalisa Colombo, Kirill A. Velizhanin, Roberto Simonutti, Nikolay S. Makarov, Victor Klimov* and Sergio Brovelli* Supplementary Discussion The efficiency of LSCs is strongly dependent on the device size, architecture (single vs. multilayer), transparency and on the use of back-reflectors or PV cells attached to the back of the slab. Our LSCs are single layered, semitransparent, with no back-reflectors, 12 cm 12 cm in size and coupled to c-si PV cells. To date, the record efficiency using c-si PVs coupled to organic based LSCs has been reported by Debije and co-workers 47 whose best device reaching 4.2% efficiency was a 5 cm 5 cm slab coupled to a MCPET back-reflector. In the same report, the authors fabricated 10 cm 10 cm stacked dual LSCs containing both Lumogen Red and blue emitting perylene-perinone. By coupling these dual devices to TiO 2 diffuse back-reflectors they achieved 2.5% efficiency. The benefits of back-reflectors are critical as they allow to recycle photons transmitted and escaped from the slab and to diffuse photons incident close to the concentrator edges directly toward the PV cells. In all cases the final LSC devices are not semitransparent because of the use of back-reflectors. Higher absolute efficiency has been achieved by Sloof et al 36 who fabricated 5 cm 5 cm LSCs based on a mixture of Lumogen red and a coumarine dye. Coupling their devices to non-standard GaAs PV cells the authors reached 5.2% efficiency. NATURE NANOTECHNOLOGY 1

2 Normalized PL Intensity/ Absorption a b c DCM Lumogen red Eu(TTA) 3 (TTPO) Wavelength (nm) Wavelength (nm) Wavelength (nm) Normalized PL Intensity/ Absorption 1.0 d Crs Yellow Wavelength (nm) e perylene perinone Wavelength (nm) f CdSe/CdS QDs Wavelength (nm) Supplementary Figure 1. Figure of merit of LSC dyes Optical absorption and photoluminescence spectra of some organic and QD LSC dyes: (a) 4-dicyanomethyl-6-dimethylaminostiryl-4H-pyran (DCM), (b) BASF Lumogen red, (c) europium tris(2-thenoyl trifluoro acetonate)- di(triphenylphosphine oxide) (Eu(TTA) 3 (TPPO) 2 ) (ref.( 48 ), (d) yellow emitting Crs040 Dye from Radiant Color, (e) a perylene perinone dye (from refs. 47,49 ) and CdSe/CdS core shell hetero-qd (shell thickness 14 monolayers, ref. 12 ) 2 NATURE NANOTECHNOLOGY 2

3 SUPPLEMENTARY INFORMATION Supplementary Figure 2. DSC curves of the pure polymer (LSC0) and CISeS QDs/P(LMA-co- EGDM) nanocomposites (LSC10 and LSC20) Differential Scanning Calorimetry (DSC) curves of the pure polymer (LSC0) and CISeS QDs/P(LMA-co-EGDM) nanocomposites (LSC10 and LSC20). First and second heating scans show a transition glass temperature (T g ) of -65 C, in good agreement with literature. Moreover, the absence of exothermic phenomena (upwards peaks) during the first heating ramp indicates that the polymerization process has proceeded to completion NATURE NANOTECHNOLOGY 3

4 Supplementary Figure 3. TGA curves of the pure polymer (LSC0) and CISeS QDs/P(LMAco-EGDM) nanocomposites (LSC10 and LSC20) TGA (Thermo-gravimetric) and DTA (differential thermo-gravimetric) curves of the pure polymer (LSC0) and CISeS QDs/P(LMA-co- EGDM) nanocomposites (LSC10 and LSC20). The weight of the residual corresponds to the amount of the QDs in the polymeric matrices: 0.3 wt.% in LSC10 and 0.5 wt.% in LSC20. 4 NATURE NANOTECHNOLOGY

5 SUPPLEMENTARY INFORMATION 1 CISeS QDs in toluene CISeS QDs in PLMA Normalized PL Intensity 0.1 Φ PL =0.21 Φ PL = Time (ns) Supplementary Figure 4. PL decays of core-only CISeS QDs in toluene and in P(LMA-co- EGDM) nanocomposites Room temperature PL decays of CISeS QDs with no further ZnS passivation in a toluene solution (black line) and in a photopolymerized QD-P(LMA-co-EGDM) nanocomposite measured using weak pulsed excitation at 405 nm. The PL quantum yield drops by about 50% upon incorporation into the polymer matrix. NATURE NANOTECHNOLOGY 5 5

6 Supplementary Fig. 5. Monte Carlo ray tracing simulation of output probability as a function of LSC area. Monte Carlo ray tracing simulation of the photon output probability in comparison to the probability of non-radiative decay and photon escape through the device surfaces for the same LSCs as in Fig.3. The simulation was performed considering QDs with photoluminescence quantum yield of (a) 40% and (b) 100%, in order to emphasize the effects of geometrical losses and light absorption by the polymer waveguide. The calculations were performed using the absorption spectrum of the final PLMA slab doped with QDs and therefore the emission losses account also for absorption by the polymer matrix. Chart plots of the outcome of the simulation are reported on the right hand side of each plot for devices with lateral dimensions of 12 cm x 12 cm and 50 cm x 50 cm. The same colour scheme applies across the whole figure. The plots highlight that for PLQY=40%, the output probability drops of only 50% by increasing the size up to 50 cm x 50 cm. The model using PLQY=100% show that such loss could be reduced to only 30% by optimizing the emission efficiency of the QDs. 6 NATURE NANOTECHNOLOGY

7 SUPPLEMENTARY INFORMATION Supplementary Figure 6. Color rendering of LSC based on Crs040 Yellow dye. a) Photograph of an LSC (12 cm 3.5 cm 0.3 cm) incorporating Crs040 Yellow dye taken with a Canon EOS 400D under ambient illumination. b) Picture of a reflecting white background taken with the same camera filtering half of the field of view with the Crs040-LSC. c) Colour rendering index (CRI) plot of original Munsell test colour samples (TCS) under D65 reference illuminant before (white dots) and after chromatic adaptation by the same LSC. Total colour rendering index R a =56.6. NATURE NANOTECHNOLOGY 7

8 100 Refelctivity (%) Crs040-LSC LSC Wavelength (nm) Supplementary Fig.7. Reflectance spectra of LSC20 and of the LSC based on Crs040 Yellow dye. Reflectance spectra of LSC20 and the LSC incorporating Crs040 Yellow dye collected using an integrating sphere and placing a Spectralon scatterer on the back side of the LSCs, following the conventional procedure for colorimetric measurements on semitransparent materials. 8 NATURE NANOTECHNOLOGY

9 SUPPLEMENTARY INFORMATION Supplementary Figure 8. Colour coordinates in CIE chromaticity space of D65 illuminant filtered using LSC20 and the LSC based on Crs040 Yellow dye. Colour coordinates in CIE chromaticity space of D65 illuminant filtered using LSC20 (grey dot) and the LSC based on Crs040 Yellow dye (yellow dot). NATURE NANOTECHNOLOGY 9

10 Supplementary Figure 9. Photoluminescence excitation spectra of CIS QDs. Photoluminescence excitation spectra (arb. Units) of 2 nm CIS QDs collected with 2.5 nm bandwidth at 555 nm, 600 nm and 655 nm. 10 NATURE NANOTECHNOLOGY

11 SUPPLEMENTARY INFORMATION Supplementary Figure 10. Pump-intensity dependence of TA decay of CIS QDs. Pumpintensity dependence of TA decay in CIS QDs measured at 500 nm (2.48 ev) under excitation with 100 fs, 3.1 ev frequency doubled pulses from an amplified Ti:sapphire laser. The excitation level is shown on the right in terms of the number of photons absorbed per QD per pulse, <N>. NATURE NANOTECHNOLOGY 11