Defect-induced betavoltaic enhancement in black titania nanotube arrays

Abstract

Utilizing high-energy beta particles emitted from radioisotopes for long-lifetime betavoltaic cells is a great challenge due to their low energy conversion efficiency (ECE). Here we report a betavoltaic cell fabricated using black titania nanotube arrays (TiO₂ NTAs) by electrochemical anodization and Ar-annealing techniques. The obtained samples show enhanced electrical conductivity as well as Vis-NIR light absorption by the introduction of oxygen vacancy (OV) and Ti³⁺ defects in reduced TiO_2−x NTAs. A 20 mCi⁶³ Ni source was assembled into TiO₂ NTAs to form a sandwich-type betavoltaic cell. By I–V measurements, the Ar-annealed TiO₂ NTAs at 650 °C exhibited a maximum ECE of 3.65% with V_oc = 1.13 V, J_sc = 103.3 nA cm⁻², and P_max = 37 nW cm⁻². In comparison with air-annealed TiO₂ NTAs, the enhancement of the betavoltaic effect in reduced TiO_2−x NTAs can be attributed to the suppression of e–h recombination induced by the generation of OV and Ti³⁺ defects, serving as electron donors as well as electron traps that not only contribute to the increase of electrical conductance, but also facilitate the charge carrier separation.