Perovskite semiconductor-engineered cascaded molecular energy levels in naturally-sensitized photoanodes

Naturally-sensitized photoanodes in dye-sensitized solar cells (DSSCs) are promising alternatives to enhance photoabsorption, electron excitation/injection, but voltage loss remains a challenge. Here, we focus on understanding the cascading of energy levels in perovskite semiconductor cosensitized naturally-sensitized photo anodes to leverage forward charge transport addressing the voltage loss arising from ITO/TiO2 heterojunction's built-in potential. The beta-carotene-sensitized TiO2 photoanode modified with methylammonium lead iodide (MAPbI(3)) co-sensitizer causes an upward shifting in TiO2 Fermi level (E-F). This phenomenon is predominantly attributed to increased initially injected electrons due to low MAPbI(3) bandgap and high visible-light absorption. Enhanced charge separation and injection mechanisms at the TiO2/MAPbI(3) interface increase the effective density-of-states (DOS 2.46 x 10(21) cm(-3)) in the TiO2 conduction band (CB) and hence decrease its work function to 4.82 eV. The decrease in TiO2 work function suppressed CB bending at ITO/TiO2 heterojunction, which minimized the photoinduced electrostatic potential barrier up to 13.1%. The reduced Schottky barrier (phi(SBH)<0.52 eV) only allows electrons tunneling, while inhibited back-electron transport reduced both current leakage and voltage loss yielding in high open-circuit voltage (V-oc increase by 120%) and power conversion efficiency (PCE increase by 240%). The MAPbI(3) incorporation also broadened photoanode absorbance by 2-fold, paving the way towards perovskite semiconductor cosensitization to avoid voltage loss from bio-integrated photoanodes for photovoltaic and other optoelectronic and photonic applications. Future works will focus on studying the series resistance, cathode electrode coating uniformity, recombination kinetics, solid electrolytes, as well as other aspects typically related to increasing the photocurrent levels of this beta-carotene-sensitized solar cell.

Automated summary

This study successfully increased the photo conversion efficiency of TiO2 photoanodes through co-sensitization. By understanding the cascading energy levels in perovskite semiconductors, voltage loss from the ITO/TiO2 heterojunction was minimized.