Supporting Information Doped Halide Perovskite Nanocrystals for Reabsorption-Free Luminescent Solar Concentrators

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1 Supporting Information Doped Halide Perovskite Nanocrystals for Reabsorption-Free Luminescent Solar Concentrators Francesco Meinardi a,b *, Quinten A. Akkerman c,d, Francesco Bruni b, Sungwook Park c,e, Michele Mauri a,b, Zhiya Dang c, Liberato Manna d *, Sergio Brovelli a,b * a Dipartimento di Scienza dei Materiali, Università degli Studi di Milano Bicocca, via R. Cozzi 55, I Milano, Italy. b Glass to Power Srl, Francesco Daverio, 6, I Milano, Italy c Dipartimento di Chimica e Chimica Industriale, Università degli Studi di Genova, via Dodecaneso 31, I-16146, Genova, Italy d Istituto Italiano di Tecnologia, via Morego 30, I Genova, Italy. e Department of Physics, Pukyong National University, Busan , Korea Corresponding Author: sergio.brovelli@unimib.it (T: ), liberato.manna@iit.it (T: ), franco.meinardi@mater.unimib.it (T: ). Methods Chemicals. Lead(II) chloride (PbCl 2, % trace metals basis), manganese(ii) chloride (MnCl 2, 99.99% trace metals basis), cesium carbonate (Cs 2 CO 3, reagentplus, 99%), octadecene (ODE, technical grade, 90%), oleylamine (OLAM, 70%) and oleic acid (OA, 90%) were purchased from Sigma-Aldrich. Toluene (TOL, anhydrous, 99.8%) was purchased from Carlo Erba reagents. All chemicals were used without any further purification. Manganese doped CsPbCl 3 NCs synthesis and purification. CsPbCl 3 NCs were synthesized as described by Protesescu et al., 6 with addition of MnCl 2. In a typical synthesis, 0.1 mmol of PbCl 2 and 0.1 mmol of MnCl 2, 5 ml ODE, 0.5 ml OA and 0.5 ml OLAM were loaded in a 25 ml 3-neck flask and dried under vacuum for 1 h at 120 C. After degassing, the temperature was raised to C and 0.4 ml of previously synthesized Cs-oleate (0.4 g Cs 2 CO 3 degassed in 15 ml ODE and 1.75 ml OA at C) was swiftly injected. 30 seconds after the injection, the NC solution was quickly cooled down to room temperature with an ice bath. The NCs were purified via centrifugation (at 3000 rpm for 30 minutes) twice, followed by redispersion in TOL. Transmission Electron Microscopy (TEM). Conventional TEM images were acquired on a JEOL JEM microscope equipped with a thermionic gun at 100 kv accelerating voltage. High-resolution TEM (HRTEM) imaging was performed on a JEOL JEM-2200FS microscope equipped with a Schottky gun operated at 200 kv accelerating voltage, a CEOS spherical aberration corrector in objective lens enabling a spatial resolution of 0.9 Å, and an in column image filter (Ω-type). Samples were prepared by drop casting diluted NC suspensions onto 200 mesh carbon-coated copper grids for conventional TEM imaging, and 400 mesh ultrathin/holey carbon-coated copper grids for HRTEM imaging, respectively. Powder X-ray Diffraction (XRD) Analysis. XRD patterns were obtained using a PANalytical Empyrean X-ray diffractometer equipped with a 1.8 kw Cu Kα ceramic X-ray tube, PIXcel3D 2x2 area detector and operating at 45 kv and 40 ma. The diffraction patterns were collected in air at room temperature using Parallel-Beam (PB) geometry and symmetric reflection mode. All XRD samples were prepared by drop casting a concentrated solution on a zero diffraction silicon wafer. Elemental Analysis. Elemental analysis was carried out via inductively coupled plasma optical emission spectroscopy (ICP-OES), using a icap 6500 Thermo spectrometer. Samples were dissolved in acqua regia. Fabrication of the nanocrystal-polymer composite 1

2 A NC powder is dispersed in a small volume of lauryl methacrylate monomer for 3 hours in order to wet the nanoparticle surface and ensure fine dispersion of the individual NCs. The monomer-nc mixture is then added to a large volume of methyl methacrylate (LMA:MMA 20%:80% w/w) and a radical photo-initiator (IRGACURE 651; 1% w/w). After stirring the mixture for 20 minutes and sonication for 10 minutes to facilitate NCs dispersion, the homogeneous mixture is poured into a mould made of two low-roughness pieces of tempered glass linked by a PVC gasket, and irradiated with 365 nm light from a UV lamp for 15 minutes, in order to trigger radical polymerization. The polymerization is then completed by keeping samples in dark for 40 minutes while leaving them in the mould in order to avoid creation of cracks. After the completion of the procedure, the slabs are removed from the mould, laser cut in pieces of desired sizes, and polished. Thermal characterization of the polymeric nanocomposite Differential Scanning Calorimetry (DSC) measurements were performed by using a Mettler Toledo DSC1 thermal analysis system equipped with a liquid nitrogen cooling unit for low temperature operation, calibrated with indium and n-pentane. For each sample, around 8 mg were sliced and placed in 40 µl Al crucibles. For analysis, we used an initial isotherm of 5 minutes to thermalize the sample at -100 C, a heating segment from -100 to 60 C, followed by cooling to -100 and heating to 100 C. Each ramp was performed at 20 K/min rate, and followed by a 3-minute isothermal equilibration step. Data analysis was performed with the Star e software. Tensile characterization of the polymeric nanocomposite Tensile properties were probed with a Zwick-Roell universal testing machine, with a 5kN cell. The sample was laser cut to prepare a rectangular prism with 4.4 mm thickness, 23 mm width and 120 to 130 mm distance between clamps. Experiment was performed in triplicates. Spectroscopic Studies All spectroscopic studies were carried out using toluene solutions of NCs loaded into quartz cuvettes and NC-PMMA/PLMA nanocomposites. In the measurements of PL dynamics, the samples were vigorously stirred to avoid the effects of photo-charging. Absorption spectra of NC solutions and NC-polymer composites were measured with a Perkin Elmer LAMBDA 950 UV/Vis/NIR spectrophotometer. PL spectra and transient PL measurements were carried out using excitation with <70 ps pulses at 395 nm from a doubled Ti:Sapphire laser. The emitted light was collected with a Si CCD camera for the photoluminescence spectra or a Hamamatsu photomultiplier tube (PMT) coupled to time-correlated single-photon counting (TCSPC) electronics (time resolution ~300ps) for the time decay dynamics. Photoluminescence quantum efficiency measurements were conducted using the same laser source at 395 nm and detection setup coupled to an integrating sphere. Specifically, the sample was mounted vertically at 45 with respect to the incident beam in anti-reflection geometry with respect to the output window, where the CCD was fibre coupled to the sphere and shielded by a buffer layer. For light scattering measurements in linear propagation configuration, 635 nm light from a laser diode was injected into the LSC edge through a 0.5 mm pin hole and the light scattered from the LSC surfaces was collected using a calibrated photodiode. Optical measurements on the one-dimensional liquid were carried out by coupling the output edge of the waveguide to an integrating sphere and using a 395 nm pulsed laser as an excitation source. For the guiding measurements on the polymer LSC under selective excitation, the device was excited perpendicularly to its top surface by either 395 nm or 410 nm light from the same tuneable laser at the same excitation flux and the PL was collected with the same CCD used for the one-dimensional LSC. Monte Carlo Ray-Tracing Simulation The simulations of the LSC performances are performed via a Monte Carlo ray tracing method, in which the photon propagation follows the geometrical optics laws. Because the LSC thickness is much larger than the light coherence length, the interference has been neglected. The stochastic nature of the simulations is reflected in the fact that the ray is not split upon reaching an interface but rather either transmitted or reflected with the probabilities proportional to respective energy fluxes given by Fresnel Laws. The dependence of these probabilities on the state of polarization of the incident ray (e.g., s- or p-polarized) is also taken into account. A specific event (i.e., transmission or reflection) is chosen according to random Monte Carlo drawing. 2

3 Monte Carlo ray-tracing simulations of the one-dimensional LSC were performed using the experimental luminescence spectrum and efficiency (Φ PL =10% for the Mn 2+ -PL and 5% for the BE-PL) of the NCs in toluene and the absorption spectrum of the solution. Inside the LSC material, for each ray, the inverse transform sampling method is applied to randomly generate the length of the optical path before absorption by NCs. Path lengths follow the exponential attenuation law determined by the wavelength-dependent absorption cross-section, σ(λ), and the NC concentration, N NC, via an attenuation coefficient, k(λ) = N NC σ(λ). Since the mean path length, given by the inverse attenuation coefficient is always much greater than the average distance between NCs, there is no need to keep track of an explicit position of each NC, so the LSC material (PMMA+ NCs) can be considered within the effective medium approach, i.e., as a uniform material with the attenuation coefficient defined above. Once a photon is absorbed by a NC, the subsequent fate of the excitation (i.e., reemission or non-radiative relaxation) is again determined by the Monte Carlo sampling according to the emission quantum yield. The direction of reemission is distributed uniformly and the reemission wavelength is determined using the rejection sampling applied to the accurate NC luminescence spectrum obtained from experiment. The ultimate fate of each photon is either loss due to non-radiative recombination or escape from the LSC via one of the interfaces. A single-ray Monte Carlo simulation is typically repeated times to have a proper statistical averaging. A stochastic nature of simulations allows one to easily evaluate various observables and add additional processes. Figure S1. DSC curve of Mn:CsPbCl 3 NCs/P(MMA/LMA) nanocomposite embedding 0.03wt% of NCs (black curve) in direct comparison with PMMA pellets. Figure S2. Mechanical analysis of a P(MMA/LMA) nanocomposite containing 0.03wt% of Mn-doped CsPbCl 3 NCs. Each curve represents an independent measurement on an identical nanocomposite sample. 3

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5 Supporting Discussion The calorimetric trace of the slab (Figure S1) indicates the presence of a small variation of specific heat around 160 C. This thermal event is compatible with a glass transition, but it is far from the glass transition clearly displayed at 115 C by reference PMMA materials. Mechanical (tensile) analysis (Figure S2) indicates that the material is hard and relatively brittle, with a tensile modulus around 1 GPa to be compared with the 1.8 to 3.1 GPa values of PMMA. The tensile modulus value, together with the higher elongation at break (5.5% vs 2.5% for standard PMMA) depict a slightly softer material as compared with most commercial PMMA materials. In this regard, the substantial amount of LMA in the monomer solution produces a polymer with local dynamics different from pure PMMA. This plurality of motional regimes renders the PMMA glass transition undetectable, explains the lower brittleness of the composite, while still allowing part of the system to relax only at 160 C. The absence of scattering (Figure 4) indicates that this variety of motional modes is not due to microscopic separation resulting in PMMA and PLMA dominated local domains. 5