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

Abstract

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 (Voc). Recently, it has been demonstrated that the Voc 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 Voc 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 Voc) in solar cells with these arrays are studied. Results show that the device Voc gradually decreases when crystallinity of shell changes from amorphous to crystalline. Moreover, the reason for a larger Voc by amorphous shell is analyzed. More dipoles could be produced at α-TiOx 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 Voc.