Luminescent solar concentrators (LSCs) are waveguides composed of a polymeric matrix doped or coated with fluorophores. The direct and/or diffuse sunlight that penetrates the matrix is absorbed by the fluorophores and then re-emitted by them with less energy. The light emitted, thanks to the total internal reflection, propagates until it reaches the edges of the wave guide where it is converted into electricity by photovoltaic cells placed on the perimeter of the matrix. The efficiency of the device is reduced by numerous loss processes, due to the reflection of the matrix and the escape cone, and/or due to the characteristics of the fluorophores, such as the absorption coefficient, the quantum yield (QY) of photoluminescence (PL) and the reabsorption. To minimize losses due to fluorophores, a good alternative are colloidal quantum dots (QDs) that usually have a high QY, a high absorption coefficient and a controllable emission wavelength by changing the size of the nanocrystals. Furthermore, by properly engineering the QDs, it is possible to realize particles with high Stokes-shift between the absorption and emission spectra, in order to reduce the reabsorption as much as possible. The project is focused on the development of the synthesis of QDs, in order to optimize the QY of photoluminescence, compatibility with the polymer matrix and photostability, while limiting the reabsorption. Besides. the synthesis procedure must be easily transferable on industrial volumes, to meet the production needs of high square meters of LSCs. During the three years of the doctoral project in High Apprenticeship I was able to develop a synthesis procedure consisting of four steps: • growth of CuInS2 core nanocrystals; • quaternary formation with zinc addition (ZnCuInS2); crucial step to increase the QY and control the emission wavelength; • growth of a zinc sulphide shell (ZnCuInS2/ZnS) to passivate the surface of nanocrystals, increase QY and photostability; • post-synthesis treatment of the partial exchange of ligands to improve solubility in the polymer matrix. The nanocrystals thus produced show 60% QY and excellent solubility in the polymer matrix. In fact, a large size LSC (30 cm x 30 cm x 0.7 cm) was produced, whose optical power efficiency, OPE = 6.8%. Initially, I developed the synthesis procedure in a 25 ml glass flask, producing 250 mg for batch. Thanks to the equipment provided by Glass to Power s.p.A I was able to study the increase in the scale of the synthesis. Firstly, in order to investigate some possible problems due to the increase in volumes, I have carried out preliminary studies on larger balloons, 500 mL and 2 L. After analysis of heating and quenching of synthesis, I have performed the synthesis in a preindustrial reactor producing 300 g of nanocrystals of ZnCuInS2/ZnS. In addition I also optimized the synthesis procedure. I tested several strategies to increase QY without damaging solubility in the polymer. Thanks to a variation of the reagent in the second step and an increase of the shell layers, I obtained nanocrystals with 80% of QY. The next step will be to scale up this new procedure and produce large LSCs. I collaborated with other PhD students, in particular, I synthesized with a heat-up method CdSe nanocrystals doped with Au7 clusters and decorated with conjugated dyes as efficient triplet sensitizers or up-conversion applications (gold doping improves up-conversion efficiency). The beneficial effects of the doping strategy result in a maximum UC efficiency of 12%, which is an unprecedented result for up-conversion based on decorated NCs as triplet sensitizers.
I concentratori solari luminescenti (LSCs) sono delle guide d’onda composti da una matrice polimerica drogata o ricoperta con fluorofori. La luce solare diretta e/o diffusa che penetra nella matrice è assorbita dai fluorofori e poi riemessa dagli stessi con energia minore. La luce emessa, grazie alla riflessione totale interna, propaga fino a raggiungere i bordi della guida d’onda dove è convertita in elettricità da celle fotovoltaiche poste sul perimetro della matrice. L’efficienza del dispositivo è ridotta da numerosi processi di perdita, sia dovuti alla riflessione della matrice e al cono di fuga, sia quelli che dipendono dalle caratteristiche dei fluorofori, come il coefficiente di assorbimento, il quantum yield (QY) di fotoluminescenza (PL) e il riassorbimento. Per minimizzare tali perdite, una buona alternativa ai tradizionali fluorofori sono i quantum dots (QDs) colloidali che presentano solitamente un elevato QY, un alto coefficiente di assorbimento e una lunghezza d’onda di emissione controllabile cambiando le dimensioni dei nanocristalli tramite modifiche dei parametri di sintesi. Inoltre, ingegnerizzando opportunamente i QDs, è possibile realizzare particelle con elevato Stokes-shift tra gli spettri di assorbimento ed emissione, in modo da ridurre quanto più possibile il riassorbimento. Il progetto si è quindi focalizzato sullo sviluppo della sintesi di QDs, al fine di ottimizzare il QY di fotoluminescenza, la compatibilizzazione con la matrice polimerica e la fotostabilità, limitando comunque il riassorbimento. Inoltre. la procedura di sintesi deve essere facilmente trasportabile su volumi industriali, per soddisfare il fabbisogno di produzioni di elevati metri quadrati di LSCs. Durante i tre anni di progetto di dottorato in Alto Apprendistato ho potuto sviluppare una procedura di sintesi che consiste in quattro step: • crescita di nanocristalli di CuInS2 core; • formazione del quaternario tramite aggiunta di zinco (ZnCuInS2); passaggio cruciale per aumentare il QY e controllare la lunghezza d’onda di emissione; • crescita di una shell di solfuro di zinco (ZnCuINS2/ZnS) per passivare la superficie dei nanocristalli, aumentare il QY e la fotostabilità; • trattamento post sintesi di scambio di leganti parziale per migliorare la solubilità nella matrice polimerica. I nanocristalli così prodotti mostrano un QY del 60% ed un’ottima solubilità nella matrice polimerica. Infatti, è stato prodotto un LSC di grande dimensione (30 cm x 30 cm x 0.7 cm) la cui optical power efficiency, OPE = 6.8%. Inizialmente ho sviluppato la procedura di sintesi in un pallone di vetro da 25 mL, producendo 250 mg a sintesi. Grazie all’attrezzatura fornita da Glass to Power S.p.A ho potuto studiare lo scale-up della sintesi. Dapprima ho effettuato studi preliminare, per approfondire alcune possibili problematiche dovute all’aumento dei volumi, su palloni di maggiori dimensioni, 500 mL e 2 L. Analizzate e risolte le tematiche di riscaldamento e stop della sintesi ho effettuato sintesi in un reattore preindustriale producendo 300 g di nanocristalli di ZnCuINS2/ZnS. Oltre ad incrementare la produzione di sintesi da 250 mg a 300 g mi sono occupata dell’ottimizzazione della procedura di sintesi. Ho testato diverse strategie per incrementare il QY senza danneggiare la solubilità nel polimero. Grazie ad una variazione di reagente nel secondo step e ad un incremento dei layer della shell ho ottenuto nanocristalli con 80% di QY. Il prossimo step sarà effettuare lo scale-up di questa nuova procedura e produrre LSC di grandi dimensioni. Grazie alle collaborazioni con altri studenti di dottorato ho sintetizzato nanocristalli di calcogenuro drogati oro e opportunamente decorati con molecole coniugate per sistemi di up-conversion. Grazie all’introduzione dell’oro in questi sistemi si è ottenuta un’efficienza di up-conversion del 12%.
(2022). Synthesis of semiconductor colloidal nanocrystals with large Stokes-shift for luminescent solar concentrators. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2022).
Synthesis of semiconductor colloidal nanocrystals with large Stokes-shift for luminescent solar concentrators
CAPITANI, CHIARA
2022
Abstract
Luminescent solar concentrators (LSCs) are waveguides composed of a polymeric matrix doped or coated with fluorophores. The direct and/or diffuse sunlight that penetrates the matrix is absorbed by the fluorophores and then re-emitted by them with less energy. The light emitted, thanks to the total internal reflection, propagates until it reaches the edges of the wave guide where it is converted into electricity by photovoltaic cells placed on the perimeter of the matrix. The efficiency of the device is reduced by numerous loss processes, due to the reflection of the matrix and the escape cone, and/or due to the characteristics of the fluorophores, such as the absorption coefficient, the quantum yield (QY) of photoluminescence (PL) and the reabsorption. To minimize losses due to fluorophores, a good alternative are colloidal quantum dots (QDs) that usually have a high QY, a high absorption coefficient and a controllable emission wavelength by changing the size of the nanocrystals. Furthermore, by properly engineering the QDs, it is possible to realize particles with high Stokes-shift between the absorption and emission spectra, in order to reduce the reabsorption as much as possible. The project is focused on the development of the synthesis of QDs, in order to optimize the QY of photoluminescence, compatibility with the polymer matrix and photostability, while limiting the reabsorption. Besides. the synthesis procedure must be easily transferable on industrial volumes, to meet the production needs of high square meters of LSCs. During the three years of the doctoral project in High Apprenticeship I was able to develop a synthesis procedure consisting of four steps: • growth of CuInS2 core nanocrystals; • quaternary formation with zinc addition (ZnCuInS2); crucial step to increase the QY and control the emission wavelength; • growth of a zinc sulphide shell (ZnCuInS2/ZnS) to passivate the surface of nanocrystals, increase QY and photostability; • post-synthesis treatment of the partial exchange of ligands to improve solubility in the polymer matrix. The nanocrystals thus produced show 60% QY and excellent solubility in the polymer matrix. In fact, a large size LSC (30 cm x 30 cm x 0.7 cm) was produced, whose optical power efficiency, OPE = 6.8%. Initially, I developed the synthesis procedure in a 25 ml glass flask, producing 250 mg for batch. Thanks to the equipment provided by Glass to Power s.p.A I was able to study the increase in the scale of the synthesis. Firstly, in order to investigate some possible problems due to the increase in volumes, I have carried out preliminary studies on larger balloons, 500 mL and 2 L. After analysis of heating and quenching of synthesis, I have performed the synthesis in a preindustrial reactor producing 300 g of nanocrystals of ZnCuInS2/ZnS. In addition I also optimized the synthesis procedure. I tested several strategies to increase QY without damaging solubility in the polymer. Thanks to a variation of the reagent in the second step and an increase of the shell layers, I obtained nanocrystals with 80% of QY. The next step will be to scale up this new procedure and produce large LSCs. I collaborated with other PhD students, in particular, I synthesized with a heat-up method CdSe nanocrystals doped with Au7 clusters and decorated with conjugated dyes as efficient triplet sensitizers or up-conversion applications (gold doping improves up-conversion efficiency). The beneficial effects of the doping strategy result in a maximum UC efficiency of 12%, which is an unprecedented result for up-conversion based on decorated NCs as triplet sensitizers.File | Dimensione | Formato | |
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phd_unimib_765562.pdf
embargo fino al 17/03/2025
Descrizione: Tesi di Capitani Chiara 765562
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Doctoral thesis
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34.68 MB
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