I've attached a Master's degree thesis which helps answer your question.

Professor Yehia Khalil, Yale University, USA

Fellow of the University of Oxford, UK

Fatemeh,

would you please give more details about the structure which do need to build? In general there is general rules for selecting the suitable materials in the front of these rules are the alignment of the energy levels to facilitate the separation and collection of the photo genearted electron hole pairs or excitons.

Best wishes

Dear Zekry

my structure is: FTO/TiO2/polymer/Al

i want band gap (TiO2 on FTO) (Dr blade) that TiO2 is Anatas dough.؟

i see in the articles TiO2 is 3.2 ev. Can I use this number for paste TiO2 on FTO (Dr blade)?!

Fatemeh,

The band gap of the TiO2 depends on the powder size used to make the paste. As the size increases the energy gap will be smaller ultimately reaching the energy gap of the bulk material. In fact this size effect is well known. It is so that as the grain size decreases the material band gain increases. The paper in the link https://pdfs.semanticscholar.org/fc37/1d67c3d7529d68d225b16f59d9d665caee55.pdf, however show that as the grain size decreases the the phoyocurrent of the cell decreases. This contradicts the increasing bandgap effect of the window layer. So, it is expected that the passed light to the absorber material increases and thereby an increase in the photocurrent.

One can understand this effect within the effect of the grain size in the porosity of the TiO2 layer. It is so that as the porosity increases, more absorber material will be included in the scaffold material. This what happens with larger grain size. As the grain size increases the material will be more porous embedding more absorber leading to larger photcurent.

If you have any further question you are welcome.

Best wishes