Carrier selective contact (CSC) material is considered promising for surface passivation applications in PV technology because it performs passivation of both non-contacted and contacted areas. Conventional heavily doped CSCs, such as n- and p-doped a-Si:H, are subjected to a few drawbacks such as significant parasitic absorption, Auger recombination, usage of toxic boron/phosphorous gas, and relatively high fabrication cost. To overcome these disadvantages and increase the power conversion efficiency (PCE) of solar cells, alternative approach is to use wide-bandgap material such as transition metal oxides (TMO) which simultaneously exhibit surface passivation, optical transparency, and carrier selectivity. These dopant-free materials could be deposited easily and economically with different deposition techniques to provide asymmetric conductivity for charge carriers. In this project, we investigated the passivation property and carrier selectivity of two types of TMOs, namely TiOx as electron transport layer (ETL) and MoOx as hole transport layer (HTL) for silicon heterojunction solar cells. The performance of TiOx based ETL is characterized by symmetrical samples for the passivation properties. The e-beam deposited TiOx induces severe damages to the passivation quality of the intrinsic amorphous silicon (i)a-Si:H layer. To mitigate the effect of TiOx several approaches were proposed aiming at minimizing the passivation degradation or recovering the part lost, namely (i)a-Si:H and (n)a-Si:H thickness, and post-deposition treatments (air annealing, H2 annealing, hydrogen plasma treatment). Among them, hydrogen plasma treatment (HPT) is the most promising with recovered initial lifetime and implied Voc up to 64% and 95%, respectively. These results suggest that the HPT treatment could be an effective method to enhance the passivation performance of the damaged c-Si/(i)a-Si:H/TiOx electron selective contact while maintaining the treatment temperature below the amorphous-to-anatase phase transformation temperature and avoid further H effusion from the (i)a-Si:H passivation layer. Performance of MoOx based HTL in SHJ solar cell is characterized by performing a temperature-dependant J-V measurement. Our study confirms that by manipulating the (i)a-Si:H interface via Plasma Treatment (PT) before MoOx, both open-circuit voltage and fill factor increase by improving the energy alignment for efficient hole transport.
Il materiale CSC (Carrier Selective Contact) è considerato promettente per la ricerca sulla passivazione superficiale perché esegue la passivazione sia delle aree non a contatto che quelle a contatto. I CSC convenzionali fortemente drogati, come a-Si:H drogati con n- e p-, sono soggetti ad alcuni inconvenienti come la significativa ricombinazione Auger, l'assorbimento parassitario, l'uso di gas tossici di boro/fosforo e il costo di produzione relativamente alto. Un approccio alternativo consiste nell'utilizzare ossidi di metalli di transizione privi di droganti (TMO) in cui, per realizzare la conduttività asimmetrica per i portatori di carica, questi strati vengono depositati con processi più semplici ed economici. In questo progetto, abbiamo studiato la proprietà di passivazione e la selettività dei portatori di due tipi di TMO, vale a dire TiOx come strato di trasporto di elettroni (ETL) e MoOx come strato di trasporto di lacune (HTL) per celle solari a etero giunzione di silicio. Le prestazioni dell'ETL a base di TiOx sono caratterizzate in campioni simmetrici per le proprietà di passivazione. Il TiOx depositato mediante la tecnica Electron-Beam induce gravi danni alla qualità di passivazione dello strato intrinseco di silicio amorfo (i) a-Si: H. Per mitigare l'effetto del TiOx sono stati proposti diversi approcci volti a ridurre al minimo la degradazione della passivazione o il recupero della parte persa, quali lo spessore di (i) a-Si:H e (n) a-Si:H, e trattamenti di post-deposizione (air annealing, H2 annealing, trattamento al plasma di idrogeno). Tra questi, il trattamento con plasma di idrogeno (HPT) è il più promettente con un recupero della vita media iniziale e Voc fino al 64% e al 95%, rispettivamente. Questi risultati suggeriscono che il trattamento HPT potrebbe essere un metodo efficace per migliorare le prestazioni di passivazione del contatto elettrone-selettivo c-Si /(i) a-Si: H /TiOx danneggiato, mantenendo la temperatura del processo al di sotto della temperatura di trasformazione di fase amorfo-anatasio ed evitando ulteriori effusioni di H dallo strato di passivazione (i) a-Si:H. Le prestazioni dell'HTL a base di MoOx nella cella solare SHJ sono caratterizzate mediante misure J-V dipendenti dalla temperatura. Il nostro studio conferma che manipolando l'interfaccia (i)a-Si:H tramite il trattamento al plasma (PT) prima dello strato depositato di MoOx, sia la tensione a circuito aperto che il fattore di riempimento aumentano migliorando l'allineamento dell'energia per un trasporto efficiente delle lacune.
Novel doping-free metal-oxide carrier selective passivating contacts for SHJ solar cells
Nikoueian, Amir Parsa
2019/2020
Abstract
Carrier selective contact (CSC) material is considered promising for surface passivation applications in PV technology because it performs passivation of both non-contacted and contacted areas. Conventional heavily doped CSCs, such as n- and p-doped a-Si:H, are subjected to a few drawbacks such as significant parasitic absorption, Auger recombination, usage of toxic boron/phosphorous gas, and relatively high fabrication cost. To overcome these disadvantages and increase the power conversion efficiency (PCE) of solar cells, alternative approach is to use wide-bandgap material such as transition metal oxides (TMO) which simultaneously exhibit surface passivation, optical transparency, and carrier selectivity. These dopant-free materials could be deposited easily and economically with different deposition techniques to provide asymmetric conductivity for charge carriers. In this project, we investigated the passivation property and carrier selectivity of two types of TMOs, namely TiOx as electron transport layer (ETL) and MoOx as hole transport layer (HTL) for silicon heterojunction solar cells. The performance of TiOx based ETL is characterized by symmetrical samples for the passivation properties. The e-beam deposited TiOx induces severe damages to the passivation quality of the intrinsic amorphous silicon (i)a-Si:H layer. To mitigate the effect of TiOx several approaches were proposed aiming at minimizing the passivation degradation or recovering the part lost, namely (i)a-Si:H and (n)a-Si:H thickness, and post-deposition treatments (air annealing, H2 annealing, hydrogen plasma treatment). Among them, hydrogen plasma treatment (HPT) is the most promising with recovered initial lifetime and implied Voc up to 64% and 95%, respectively. These results suggest that the HPT treatment could be an effective method to enhance the passivation performance of the damaged c-Si/(i)a-Si:H/TiOx electron selective contact while maintaining the treatment temperature below the amorphous-to-anatase phase transformation temperature and avoid further H effusion from the (i)a-Si:H passivation layer. Performance of MoOx based HTL in SHJ solar cell is characterized by performing a temperature-dependant J-V measurement. Our study confirms that by manipulating the (i)a-Si:H interface via Plasma Treatment (PT) before MoOx, both open-circuit voltage and fill factor increase by improving the energy alignment for efficient hole transport.| File | Dimensione | Formato | |
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Amir Parsa Nikoueian -Novel Doping-Free Metal-Oxide Carrier Selective Passivating Contacts for SHJ Solar Cells- Submited Thesis report.pdf
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https://hdl.handle.net/10589/174959