The field of organic photovoltaic materials has been a hot topic for the scientific research during the last decade due to its promising application in relieving energy pressure and environmental problems. Compared to the most used inorganic ones, they are easier to fabricate, cheaper and more eco-friendly. However, organic semiconductors are affected by limitations in the transport process, resulting in maximum efficiencies achieved so far that are not enough to substitute the widely spread Silicon PV solar cell. Trying to solve this issue, a novel energy harvesting device was presented in 2012: the Light Harvesting Capacitor (LHC), where photovoltaic energy conversion is based on the generation of nano-dipoles at interfaces, without relying on charge carrier transport through the active layer. This master thesis will focus on the study, fabrication and characterization of Hybrid Perovskite LHCs (Pe-LHCs), introducing for the first time methylammonium lead iodide in the device architecture, thanks to its remarkable photovoltaic performance, with solution processed perovskite solar cells exceeding 20% of conversion efficiency. The starting point was the study of the reference LHC structure based on CuPc and fullerene as a donor-acceptor couple. After that, the focus switched to the introduction of perovskite and different layers stacking combinations and configurations were studied, with the final purpose to create and test the most efficient device. Regarding the fabrication, the materials employed for the active layer were thermally evaporated or spin-coated on top of the insulant layer and then enclosed in an additional one. In order to understand the behavior of the different devices, their absorption spectra were studied, before testing all the structures under light and dark cycles and measuring the time-resolved current generated. The transient photo- current was integrated to obtain the stored charge allowing the computation of the final external efficiency. Although the values obtained were rather far from the original reference device ones, indicating a necessary optimization of the overall device, good results were obtained from the incorporation of MAPbI3 in the LHC structure. With the most efficient device a study of the performance dependence on wavelength and light intensity was done: some difficult to interpret results were found, indicating that further studies need to be done on this nonetheless promising device.
Nel corso dell’ultimo decennio i materiali organici fotovoltaici sono stati al centro della ricerca scientifica, grazie alle loro promettenti applicazioni nella mitigazione del fabbisogno energetico e dei problemi ambientali. Nonostante siano più facili da fabbricare, economici ed eco-compatibili dei più comuni materiali inorganici, essi sono affetti da limitazioni nel processo di trasporto. Di conseguenza, le massime efficienze raggiunte finora non sono sufficienti per la sostituzione del silicio. Cercando di risolvere questo problema, nel 2012 è stato presentato un nuovo dispositivo per la raccolta di energia: il Light Harvesting Capacitor (LHC), in cui il processo fotovoltaico si basa sulla generazione di nano-dipoli alle interfacce, senza fare affidamento sul trasporto di carica nello strato attivo. Questa tesi magistrale si concentrerà su studio, fabbricazione e caratterizzazione di LHCs in perovskite ibrida, introducendo per la prima volta lo ioduro di piombo metilammonio nell'architettura del dispositivo, motivata dalle notevoli prestazioni fotovoltaiche che hanno portato le celle solari a perovskite ad ottenere efficienze di conversione di oltre 20%. Il punto di partenza è stato lo studio della struttura LHC di riferimento, basata su CuPc e C60 come coppia donatore-accettore. Successivamente la perovskite è stata introdotta e sono state studiate diverse combinazioni e configurazioni dei vari strati di materiale, con lo scopo finale di creare e testare il dispositivo più efficiente. Per quanto riguarda la fabbricazione, i materiali attivi impiegati sono stati evaporati termicamente o depositati tramite spin-coating su di uno strato isolante e ricoperti con un ulteriore strato. Per comprendere il comportamento dei diversi dispositivi sono stati studiati i loro spettri di assorbimento. In seguito le strutture sono state testate con cicli di luce-buio, la corrente generata nel tempo è stata misurata ed integrata per ottenere la carica immagazzinata e consentire il calcolo dell'efficienza esterna. Sebbene i valori ottenuti siano piuttosto lontani da quelli della struttura di riferimento, indicando la necessaria ottimizzazione del dispositivo nel suo complesso, buoni risultati sono stati ottenuti dall'incorporazione di MAPbI3. Con il dispositivo più efficiente è stato condotto uno studio sulla dipendenza delle prestazioni in termini di lunghezza d'onda ed intensità luminosa: i risultati ottenuti sono di difficile interpretazione, indicando la necessità di ulteriori studi su questo dispositivo.
Hybrid perovskite light harvesting capacitors (Pe-LHCs)
BONDELLI, GAIA
2017/2018
Abstract
The field of organic photovoltaic materials has been a hot topic for the scientific research during the last decade due to its promising application in relieving energy pressure and environmental problems. Compared to the most used inorganic ones, they are easier to fabricate, cheaper and more eco-friendly. However, organic semiconductors are affected by limitations in the transport process, resulting in maximum efficiencies achieved so far that are not enough to substitute the widely spread Silicon PV solar cell. Trying to solve this issue, a novel energy harvesting device was presented in 2012: the Light Harvesting Capacitor (LHC), where photovoltaic energy conversion is based on the generation of nano-dipoles at interfaces, without relying on charge carrier transport through the active layer. This master thesis will focus on the study, fabrication and characterization of Hybrid Perovskite LHCs (Pe-LHCs), introducing for the first time methylammonium lead iodide in the device architecture, thanks to its remarkable photovoltaic performance, with solution processed perovskite solar cells exceeding 20% of conversion efficiency. The starting point was the study of the reference LHC structure based on CuPc and fullerene as a donor-acceptor couple. After that, the focus switched to the introduction of perovskite and different layers stacking combinations and configurations were studied, with the final purpose to create and test the most efficient device. Regarding the fabrication, the materials employed for the active layer were thermally evaporated or spin-coated on top of the insulant layer and then enclosed in an additional one. In order to understand the behavior of the different devices, their absorption spectra were studied, before testing all the structures under light and dark cycles and measuring the time-resolved current generated. The transient photo- current was integrated to obtain the stored charge allowing the computation of the final external efficiency. Although the values obtained were rather far from the original reference device ones, indicating a necessary optimization of the overall device, good results were obtained from the incorporation of MAPbI3 in the LHC structure. With the most efficient device a study of the performance dependence on wavelength and light intensity was done: some difficult to interpret results were found, indicating that further studies need to be done on this nonetheless promising device.| File | Dimensione | Formato | |
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2018_10_Bondelli.pdf
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https://hdl.handle.net/10589/142802