A component that is able to transport charges while being transparent to light is fundamental in many devices, form LCD screens to touch panels and solar cells. The most diffuse transparent electrode material is Indium Tin Oxide (ITO) grace to its high performances, but the costly production techniques, indium rarity and the inherent fragility are pushing the market to look for alternatives. An ideal ITO substitute should provide high performances, inexpensive wet-based production techniques, low raw material cost and the possibility to be applied to flexible devices. In this work, a method for the creation of a junctionless metal nanowire network as transparent electrode using electrospinning and electroless deposition is proposed, with no annealing steps needed as in conventional nanowire production. The method exploits the insertion of the electroless sensitizing agent into the electrospinning solution in order to selectively catalyze the metallization of the electrospun nanofiber template. In the first part of the research the electrospinning process of PVB was extensively studied and the conditions that allow to produce the smallest polymeric core were identified. In the second part of the research the metallization of nickel and copper via hypophosphite based baths was explored. Whereas for Ni the results were unsatisfactory, Cu showed to be a viable solution and hence the influence of the fiber density and plating time on electrodes performances and deposit morphology were studied. The best optoelectronic properties achieved are already close to ITO and to the limit for most applications, namely Rs 35 = for T 90% with very flat transmittance window. The survey on surface roughness and the corrosion stability showed that improvements are needed in these two areas to ensure a ready integration. A cyclic bending test proved the electrodes to give optimal behavior on flexible substrates if compared to ITO. Ultimately, the effectiveness of the proposed annealing-free, wet-based, and scalable production method was demonstrated, opening new possibilities for the realization of efficient nanowire networks as ITO replacement.
La presenza di un componente che sia in grado di trasportare cariche e contemporaneamente essere trasparente alla luce è fondamentale in molti dispositivi, dagli schermi LCD ai pannelli touchscreen e alle celle solari. Grazie alle sue prestazioni elevate il materiale più diffuso oggigiorno è l’ossido di indio e stagno (Indium Tin Oxide, ITO), ma gli ingenti costi di produzione, la rarità dell’indio e la fragilità intrinseca stanno spingendo il mercato a cercare alternative. Nel presente lavoro è proposto un metodo che fa uso dell’elettrofilatura e della deposizione autocatalitica per la creazione di un network di nanofili metallici privo di giunzioni come elettrodo trasparente, senza trattamenti di annealing richiesti. Il presente metodo sfrutta l’inserimento dell’agente sensibilizzante della deposizione autocatalitica nella soluzione di elettrofilatura in modo tale da catalizzare la sola metallizzazione del template polimerico elettrofilato. Nella prima parte della ricerca è stato ampiamente studiato il processo di elettrofilatura di PVB e sono state identificate le condizioni di produzione del più piccolo core polimerico. Nella seconda parte della ricerca è stata esplorata la metallizzazione di nichel e rame. Mentre i risultati con nichel sono stati deludenti, il rame ha mostrato di essere una soluzione percorribile; l’influenza della densità di fibre e tempo di metallizzazione sulla morfologia del deposito e sulle prestazioni degli elettrodi sono state quindi studiate. Le migliori proprietà optoelettroniche ottenute (Rs 35 = per T 90 %) sono vicine a quelle dell’ITO e al limite richiesto per la maggior parte delle applicazioni, con una finestra di trasmittanza molto piatta. L’indagine condotta sulla rugosità superficiale e sulla stabilità in aria ha mostrato che alcuni miglioramenti sono necessari in queste due aree, mentre un esperimento di deformazione ciclica ha mostrato le proprietà superiori degli elettrodi su substrati flessibili se comparati a ITO. L’efficacia di un metodo economico, che consente l’applicazione su dispositivi flessibili e con elevate prestazioni è stata quindi dimostrata, aprendo nuove possiblità per la realizzazione di elettrodi basati su nanofili metallici come rimpiazzo dell’ITO.
Flexible and transparent nanowire electrodes via electroless metallization of electrospun nanofibers
TESTA, ANDREA
2014/2015
Abstract
A component that is able to transport charges while being transparent to light is fundamental in many devices, form LCD screens to touch panels and solar cells. The most diffuse transparent electrode material is Indium Tin Oxide (ITO) grace to its high performances, but the costly production techniques, indium rarity and the inherent fragility are pushing the market to look for alternatives. An ideal ITO substitute should provide high performances, inexpensive wet-based production techniques, low raw material cost and the possibility to be applied to flexible devices. In this work, a method for the creation of a junctionless metal nanowire network as transparent electrode using electrospinning and electroless deposition is proposed, with no annealing steps needed as in conventional nanowire production. The method exploits the insertion of the electroless sensitizing agent into the electrospinning solution in order to selectively catalyze the metallization of the electrospun nanofiber template. In the first part of the research the electrospinning process of PVB was extensively studied and the conditions that allow to produce the smallest polymeric core were identified. In the second part of the research the metallization of nickel and copper via hypophosphite based baths was explored. Whereas for Ni the results were unsatisfactory, Cu showed to be a viable solution and hence the influence of the fiber density and plating time on electrodes performances and deposit morphology were studied. The best optoelectronic properties achieved are already close to ITO and to the limit for most applications, namely Rs 35 = for T 90% with very flat transmittance window. The survey on surface roughness and the corrosion stability showed that improvements are needed in these two areas to ensure a ready integration. A cyclic bending test proved the electrodes to give optimal behavior on flexible substrates if compared to ITO. Ultimately, the effectiveness of the proposed annealing-free, wet-based, and scalable production method was demonstrated, opening new possibilities for the realization of efficient nanowire networks as ITO replacement.| File | Dimensione | Formato | |
|---|---|---|---|
|
main.pdf
non accessibile
Descrizione: Thesis text
Dimensione
147.24 MB
Formato
Adobe PDF
|
147.24 MB | Adobe PDF | Visualizza/Apri |
I documenti in POLITesi sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/10589/115262