In this work we focused on the improvement of pin perovskite solar cells (PSCs) efficiency and stability by exploring the possibility to integrate industrial-scalable graphene flakes (GF) into the photovoltaic devices. The optoelectronic properties, the low cost and reproducible synthesis production make GFs good candidate as additive in the photovoltaic devices, compatible with PSC industrial exploitation. The GF integration was investigated in each different layer of the pin device, showing positive effects when added into the phenyl-C61-butyric acid methyl ester (PCBM) electron transporting layer (ETL) to form a GF:PCBM composite matrix. The GF addition into the ETL enhanced the VOC and FF figures of merit of the devices, leading to a record efficiency of 20.77%, and an average PCE value 11.41% higher than the reference device. Also, the GF:PCBM devices showed enhanced stability by retaining 91.5% of the initial PCE, tested in inert ambient under continuous illumination (1 Sun) for 3800 minutes. The physical chemistry characterizations conducted on the GF:PCBM material (PLQY, TrPL) and on the devices (TPV, VOC/Light Intensity) highlighted the positive role that GF play at the perovskite/ETL interface of the devices, by acting as perovskite surface defect passivator and enhancing the charge carries extraction. Furthermore, the validity of this approach has been proved in another PSC configuration, in which the GF:PCBM ETL has been formed on top of the perovskite layer passivated with 2D cation. The GF addition into PCBM resulted into enhanced performances also with the presence of the 2D perovskite passivant, achieving the best efficiency of 20.70% and a mean PCE growth of 2.41% with respect to the reference solar cells with 2D passivation. Lastly, the GF material has been used to form a graphene based bulky ETL, in order to substitute the expensive PCBM in the transporting layer, showing a mean PCE value of 6.80%. Even though this approach still lacks in efficiency, the consistent and reproducible performances showed by the devices pave the way to further research on the use of graphene based materials for PCBM-free ETL.
In questo lavoro ci focalizziamo sul miglioramento dell'efficienza e della stabilità delle celle solari a perovskite (PSC) a configurazione invertita (pin) esplorando la possibilità di integrare flakes di grafene (GF) sintetizzabili a livello industriale all’interno dei dispositivi fotovoltaici. Le proprietà optoelettroniche, il basso costo e il processo di sintesi riproducibile candidano i GF come promettenti materiali additivi nei dispositivi fotovoltaici, compatibili con l’espansione industriale delle PSC. L’integrazione del grafene è stata esplorata in ogni strato costituente il dispositivo riportando effetti positivi quando effettuata all’interno dello strato trasportatoti di elettroni (ETL), costituito dall’estere metilico dell'acido fenil-C61-butirrico (PCBM), per formare una matrice composita di GF:PCBM. L’inclusione dei GF promuove l’aumento di Voc e FF portando a un'efficienza record del 20,77% e a un valore medio di PCE superiore dell'11,41% rispetto ai dispositivi di riferimento. Anche la stabilità, misurata in ambiente inerte sotto continua illuminazione (1 Sun), risulta migliorata in seguito all’integrazione dei GF mantenendo il 91.5% del valore di efficienza iniziale. Le caratterizzazioni chimico fisiche eseguite sul materiale GF:PCBM ( PLQY, TrPL) e sui dispositivi (TPV, Voc/Intensità di luce) svelano il ruolo positivo svolto dai GF all’interfaccia perovskite/ETL delle celle solari, attuato attraverso la passivazione dei difetti di superficie della perovskite e la più rapida estrazione di carica. Inoltre, la validità dell’approccio proposto è stata verificato in una differente configurazione di PSC, nella quale il GF:PCBM ETL è posto al di sopra dello strato di perovskite passivato con un catione 2D. Anche in presenza della perovskite 2D passivante, l’aggiunta del grafene promuove aumento dell’efficienza ottenendo un valore record del 20.70% e un aumento medio del 2.41% rispetto alle celle solari di riferimento con passivazione 2D. Infine, al fine di sostituire il costoso PCBM, i GF sono stati adoperati per la formazione di un ETL a base di grafene, ottenendo celle solari con un valore di PCE medio del 6.80%. Nonostante i limitati valori di efficienza ottenuti con tale approccio, le prestazioni coerenti e riproducibili mostrate dai dispositivi aprono la strada a ulteriori ricerche sull'uso di materiali a base di grafene per ETL privi di PCBM.
Esplorazione e ingegnerizzazione dell’uso di flakes di grafene per l’aumento dell’efficienza delle celle solari a perovskite
BULFARO, ISABELLA
2021/2022
Abstract
In this work we focused on the improvement of pin perovskite solar cells (PSCs) efficiency and stability by exploring the possibility to integrate industrial-scalable graphene flakes (GF) into the photovoltaic devices. The optoelectronic properties, the low cost and reproducible synthesis production make GFs good candidate as additive in the photovoltaic devices, compatible with PSC industrial exploitation. The GF integration was investigated in each different layer of the pin device, showing positive effects when added into the phenyl-C61-butyric acid methyl ester (PCBM) electron transporting layer (ETL) to form a GF:PCBM composite matrix. The GF addition into the ETL enhanced the VOC and FF figures of merit of the devices, leading to a record efficiency of 20.77%, and an average PCE value 11.41% higher than the reference device. Also, the GF:PCBM devices showed enhanced stability by retaining 91.5% of the initial PCE, tested in inert ambient under continuous illumination (1 Sun) for 3800 minutes. The physical chemistry characterizations conducted on the GF:PCBM material (PLQY, TrPL) and on the devices (TPV, VOC/Light Intensity) highlighted the positive role that GF play at the perovskite/ETL interface of the devices, by acting as perovskite surface defect passivator and enhancing the charge carries extraction. Furthermore, the validity of this approach has been proved in another PSC configuration, in which the GF:PCBM ETL has been formed on top of the perovskite layer passivated with 2D cation. The GF addition into PCBM resulted into enhanced performances also with the presence of the 2D perovskite passivant, achieving the best efficiency of 20.70% and a mean PCE growth of 2.41% with respect to the reference solar cells with 2D passivation. Lastly, the GF material has been used to form a graphene based bulky ETL, in order to substitute the expensive PCBM in the transporting layer, showing a mean PCE value of 6.80%. Even though this approach still lacks in efficiency, the consistent and reproducible performances showed by the devices pave the way to further research on the use of graphene based materials for PCBM-free ETL.È consentito all'utente scaricare e condividere i documenti disponibili a testo pieno in UNITESI UNIPV nel rispetto della licenza Creative Commons del tipo CC BY NC ND.
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https://hdl.handle.net/20.500.14239/14832