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

Abstract

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 photoanodes to leverage forward charge transport addressing the voltage loss arising from ITO/TiO2 heterojunction's built-in potential. The β-carotene-sensitized TiO2 photoanode modified with methylammonium lead iodide (MAPbI3) co-sensitizer causes an upward shifting in TiO2 Fermi level (EF). This phenomenon is predominantly attributed to increased initially injected electrons due to low MAPbI3 bandgap and high visible-light absorption. Enhanced charge separation and injection mechanisms at the TiO2/MAPbI3 interface increase the effective density-of-states (DOS >2.46 × 1021 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 (φSBH<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 (Voc increase by 120%) and power conversion efficiency (PCE increase by 240%). The MAPbI3 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 β-carotene-sensitized solar cell.