Changes of Voc in Hybrid Solar Cells by TiO2 Nanoarray with Different Crystallinity of Shell.

Polymer-inorganic hybrid solar cells with pure vertically aligned TiO₂ nanorod arrays (TiO₂-NRA) normally suffer from a rather low (<0.4 V) open-circuit voltage (V_oc). Recently, it has been demonstrated that the V_oc in polymer/TiO₂-NRA solar cells can be improved to 0.7 V by formation of homostructured core-shell structures with single-crystalline TiO₂ nanorod as core and the polycrystalline TiO₂ quantum dots aggregation layer as shell. However, the V_oc was not achieved high enough, and effects of different crystallinity of shell on device performance have not been investigated. In this paper, we obtained three types of homostructured TiO₂ core-shell nanoarrays with different crystallinity of TiO₂ shell (amorphous, amorphous&crystalline, and polycrystalline) through controlling shell reaction time. The changes of device performance (in particular, the V_oc) in solar cells with these arrays are studied. Results show that the device V_oc gradually decreases when crystallinity of shell changes from amorphous to crystalline. Moreover, the reason for a larger V_oc by amorphous shell is analyzed. More dipoles could be produced at α-TiO_x shell/polymer interface than crystalline TiO₂ shell/polymer interface, which results in a further up-shifting conduction band edge in TiO₂ nanorod core toward the local vacuum level of the polymer, along with a further enhanced V_oc. [ABSTRACT FROM AUTHOR]