Nanoscale visualization of hot carrier generation and transfer at non-noble metal and oxide interface

Abstract

• We provide an experimental evidence to realize the hot carrier generation and their injection at nanoscale from a non-noble metal to a metal oxide layer. • The ultrafast decay signature (τ 2 = 1.4 ps) and strong photo-bleaching signal over a wide spectral range are observed. • The hot carrier generation and injection efficiency can be increased by using a double layer of non-noble metal. • The present study can be easily integrated into existing planar structure for direct visualization and mapping of carrier injection and paves the way for increasing the PCE of PV devices. The conversion efficiency of energy-harvesting devices can be increased by utilizing hot-carriers (HCs). However, due to ultrafast carrier-carrier scattering and the lack of carrier injection dynamics, HC-based devices have low efficiencies. In the present work, we report the effective utilization of HCs at the nanoscale and their transfer dynamics from a non-noble metal to a metal oxide interface by means of real-space photocurrent mapping by using local probe techniques and conducting femtosecond transient absorption (TA) measurements. The photocurrent maps obtained under white light unambiguously show that the HCs are injected into the metal oxide layer from the TiN layer, as also confirmed by conductive atomic force microscopy. In addition, the increased photocurrent in the bilayer structure indicates the injection of HCs from both layers due to the broadband absorption efficiency of TiN layer, passivation of the surface states by the top TiN layer, and smaller barrier height of the interfaces. Furthermore, electrostatic force microscopy and Kelvin probe force microscopy provide direct evidence of charge injection from TiN to the MoO x film at the nanoscale. The TA absorption spectra show a strong photo-bleaching signal over wide spectral range and ultrafast decaying behavior at the picosecond time scale, which indicate efficient electron transfer from TiN to MoO x . Thus, our simple and effective approach can facilitate HC collection under white light, thereby achieving high conversion efficiency for optoelectronic devices.