Ultrafast laser dynamics of metal organic frameworks/TiO₂ nano-arrays hybrid composites for energy conversion applications

Herein, we report the victorious synthesis of metal-organic frameworks (MOFs) on TiO₂ nanotubes (NTs) using a layer-by-layer (LbL) approach. Highly crystalline and homogenous thin films of MOFs were grown and characterized using XRD, SEM, FT-IR and UV/Vis spectroscopy. Moreover, the utilization of the MOF films as sensitizers was probed in bespoke Graetzel type liquid junction solar cells. The constructed cell performance revealed an I_sc of 1.16 mA cm^–2, V_oc of 0.63 V, FF of 0.33, and E_ff of 0.42%. Further, pump-probe transient laser spectroscopy was performed to investigate the energy and charge transfer dynamics of the MOFs/TiO₂ NTs interface. The results indicated 86% injection efficiency. The ultrafast pump-probe spectroscopy allows the investigation of this process and the differences between MOFs. It also showed that the relaxation of the MOF chromophores is in competition with electron injection in the TiO₂ motif. Thus this study provides a new insight into electron transfer from photoexcited metal-organic frameworks (MOFs) into titanium dioxide.