| AVS 65th International Symposium & Exhibition | |
| Applied Surface Science Division | Thursday Sessions |
| Session AS+SE-ThM |
| Session: | Applied Surface Analysis of Novel, Complex or Challenging Materials |
| Presenter: | Vincent Fernandez, Université de Nantes, Institut des matériaux Jean Rouxel, France |
| Authors: | S. Bechu, Institut Photovoltaïque d’Ile-de-France N. Fairley, Casa Software Ltd, UK L. Brohan, Institut des materiaux Jean Rouxel, France V. Fernandez, Université de Nantes, Institut des matériaux Jean Rouxel, France M. Richard-Plouet, Institut des matériaux Jean Rouxel, France |
| Correspondent: | Click to Email |
1. Introduction
Third generation solar cells aims at increasing efficiency to overtake the 31% theoretical efficiency of simple junction photovoltaic cells established by Shockley and Queisser . According to Marti and Luque [1] , intermediate band cell concept could increase the photocurrent via the absorption of sub-bandgap photons without degrading the voltage. In this perspective, we developed hybrid photosensitive sols-gels based on titanium complexes with specific optical and electronic properties [2] . Once illuminated under UV light, an intermediate band (IB) appears in the band structure so the absorption spreads over visible to near infrared due to reduction of Ti(IV) in Ti(III) [3] and leads to several important changes in the titanium oxide based nanomaterial chemistry. Thanks to this absorption range increase, these gels could be used as active layers in solar cells.
2. Analysis applied to characterize chemical modifications
In order to get insight in the chemical modifications induced by the creation of the IB, XPS experiments were conducted on thin films while UV illumination was performed in situ. We present here a new mathematical method which can be applied to XPS measurements when an evolving set of data is recorded: the vectorial method [4,5]. In this case this method is applied simultaneously to Ti 2p and O 1s XPS peaks [6]. From the data set analysis, we established that each of the two Ti(IV) and Ti(III) signals can be split into two components: one Ti(IV) at 458.4 eV is associated to one Ti(III) at 457.1 eV whereas, under UV illumination, a second Ti(IV) peak appears and evolves similarly than a second Ti(III) peak, at 458.1 and 456.7 eV respectively. Those features were obtained from the vectorial method. It was successfully applied to in situ UV illumination allowing to get the percentage of thin films photoreduction, the chemical state appearing upon illumination and evolution.
[1] A. Luque and A. Martí, Phys. Rev. Lett. 78, 5014 (1997).
[2] Cottineau Thomas, Brohan Luc, Pregelj Matej, Cevc Pavel, Richard‐Plouet Mireille, and Arčon Denis, Advanced Functional Materials 18, 2602 (2008).
[3] T. Cottineau, A. Rouet, V. Fernandez, L. Brohan, and M. Richard-Plouet, J. Mater. Chem. A 2, 11499 (2014).
[4] J. Baltrusaitis, B. Mendoza-Sanchez, V. Fernandez, R. Veenstra, N. Dukstiene, A. Roberts, and N. Fairley, Applied Surface Science 326, 151 (2015).
[5] M. d’Halluin, T. Mabit, N. Fairley, V. Fernandez, M. B. Gawande, E. Le Grognec, and F.-X. Felpin, Carbon 93, 974 (2015).
[6] S. Béchu, B. Humbert, V. Fernandez, N. Fairley, and M. Richard-Plouet, Applied Surface Science 447, 528 (2018).