Upconverter loaded MoS₂ counter electrode for broadband dye-sensitized solar cell applications

An interesting approach of including an upconverter in the MoS₂ counter electrode can yield broadband light harvesting Pt-free DSSC assembly. Here different upconverter (UC) nanoparticles (Yb, Er incorporated NaYF₄, YF₃, CeO₂ & Y₂O₃) were synthesized and loaded in MoS₂ thin film by hydrothermal method. The inclusion of UCs in MoS₂ films exposed without any secondary formation of upconverters and the uniform deposition of the films are confirmed through XRD and FESEM analysis respectively. The absorption spectrum (UV-Vis-NIR) confirms the increase in absorption intensity in visible and NIR regions due to the incorporation of UCs. Under 980 nm excitation, the UCs-loaded MoS₂ films show emission in blue (450-490 nm), green (520-540 nm) and red (600-700 nm) regions due to the f-f inner transition occurring in the Er ions. The oxide and fluoride UCs-based DSSCs were fabricated with an FTO/TiO₂/N719/Triiodide electrolyte/UC@MoS₂/FTO assembly. Oxide UCs show greater electrocatalytic activity, which might be owed to the films exposed with more catalytic active sites favourable for ion transportation in the I^-/I^- ₃ electrolyte. Among them, higher photoconversion efficiency (PCE) of 7.1% was witnessed for (Y₂O₃: Er, Yb) @MoS₂ counter electrode-based DSSC which is due to the good conductivity (R_S) of the film, the longer electron lifetime and photon harvesting enhancement by upconversion process. It is notably convinced that the UC-loaded MoS₂ films can be used as an effective counter electrode for the possible realization of upconverter DSSC and used for broadband light absorption.