Facile in situ synthesis of dendrite-like ZnO/ZnTe core/shell nanorod heterostructures for sensitized solar cells

Abstract

ZnTe, a non-toxic low band gap semiconductor, has a direct band gap of 2.26 eV, and can be a promising candidate for non-toxic semiconductor sensitized solar cells (SSSCs). Herein, we report a simple and low-cost solution-processing approach to synthesize ZnTe nanocrystals by using dendrite-like ZnO nanorods as templates via an in situ method for application in solar cells. Structural and morphological analyses and systematic optical property investigations evidenced the successful synthesis of ZnTe nanocrystals and ZnO/ZnTe heterostructures. The measured band alignment of the heterostructures directly points to the strong effect of strain and the possibility to engineer the band offset at the ZnO/ZnTe interface. As ZnO and ZnTe exhibit a type-II energy level alignment, both significant absorption and efficient charge transfer are enabled between the two. Finally, solar cells based on the ZnO/ZnTe heterostructure were fabricated and a short-circuit photocurrent density of over 5 mA cm⁻² was achieved, benefiting from the preeminent absorption, high charge separation and transfer efficiency. A ZnS passivation layer dramatically improved the performance of the solar cells reaching a short-circuit photocurrent density of over 10 mA cm⁻², along with an increase in the power conversion efficiency (PCE) from 0.46% to 1.7%. Potential pathways towards further increasing this figure are discussed.