Enhanced Photocurrent Density by Spin-Coated NiO Photocathodes for N-Annulated Perylene-Based p-Type Dye-Sensitized Solar Cells

The low photocurrent density of p-type dye-sensitized solar cells (p-DSSCs) has limited the development of high-efficiency tandem cells due to the inadequate light-harvesting ability of sensitizers and the low hole mobility of semiconductors. Hereby, two new "push-pull" type organic dyes (PQ-1 and PQ-2) containing N-annulated perylene as electron donor have been synthesized, where the PQ-2-based p-DSSCs show higher photoelectric conversion efficiency (PCE) of 0.316% owing to the higher molar extinction compared to of that PQ-1. Additionally, the photocurrent densities were remarkably increased from 2.20 to 5.85 mA cm^-2 for PQ-1 and 2.45 to 6.69 mA cm^-2 for PQ-2 by spin-coated NiO photocathode based-p-DSSCs, respectively. This results are ascribed to the enhancement of hole transport rate, dye-loading amounts and transparency of NiO films in comparison to that prepared by screen-printing method. Electrochemical impedance spectroscopy and theoretical calculations studies indicate that the molecular dipole moment approaching closer to the NiO surface shifts the quasi-Fermi level to more positive levels, improving open-circuit voltage (V_oc). Intensity-modulated photocurrent spectroscopy illustrates that the hole transit time in NiO films prepared in spin-coating is shorter than that prepared by screen-printing method.