Independent Research Proposal:
Transition metal dichalcogenide (TMD) nanoflake thin films are attractive electrode materials for photoelectrochemical (PEC) solar energy conversion and sensing applications, but their photocurrent quantum yields are generally lower than bulk TMD electrodes. In this seminar, I will discuss a single nanoflake photocurrent mapping approach to reveal how doping heterogeneity limits ensemble-level PEC performance. Photocurrent mapping of MoS2 nanoflakes exfoliated from naturally occurring bulk crystals revealed the presence of n- and p-type domains within the same nanoflake. At the single domain-level, the n- and p-type domains were equally efficient for iodide oxidation and tri-iodide reduction.. This single domain-level behavior helps to explain the poor performance at the ensemble-level. Individual n- and p-type domains oppose each other when illuminated, resulting in low to zero photocurrent. The doping heterogeneity effect is likely due to non-ideal stoichiometry, where p-type domains are S-rich according to XPS measurements. While this doping heterogeneity effect limits photoanode or photocathode performance, these findings open the possibility to synthesize efficient TMD nanoflake photocatalysts with well-defined lateral p- and n-type domains for enhanced charge separation.