Energy level alignment at interfaces is critical for fundamental understanding and optimization of organic photovoltaics (OPV) as band offsets of the donor and acceptor materials largely determine the open circuit voltage (Voc) of the device. Using ultraviolet photoemission spectroscopy (UPS) and inverse photoemission spectroscopy (IPS), we examined the correlation between energy level alignment and photovoltaic properties of a model bilayer hybrid solar cell incorporating electrodeposited polythiophene (e-PT) films on ZnO planar substrates. The electrolyte anion (BF4−, PF6−, ClO4− or CF3SO3−) in the electrodeposition solution was found to have a strong influence on the e-PT film morphology and adhesion, the energy level alignment at the interface, and ultimately the Voc of the photovoltaic devices.

Integrating polymers with inorganic nanostructures is difficult due to wetting and surface energy considerations. In this paper, we developed an electropolymerization method to grow conformal polymers on high aspect ratio nanostructures. Our method is shown to improve the polymer filling rate inside the nanostructures and can be used in the development of efficient hybrid solar cells. As an example, we have studied the hybrid system of electropolymerized polythiophene (e-PT) on ZnO planar and nanorod substrates using surface characterization methods. Although unsubstituted polythiophene is not the ideal polymer material for high efficiency solar cells, it is an excellent choice for studying basic bonding and morphology in hybrid structures. We find that e-PT is covalently bound to the polar ZnO planar substrate via a Zn–S bond, adopting an upright geometry. By contrast, no strong covalent bonding was observed between e-PT and ZnO nanorods that consist of nonpolar ZnO surfaces predominantly. We manipulated the polymer morphology along the ZnO nanorods by tuning the polarity of the solvent used in electropolymerization. Our electropolymerization approach to integrate the organic and inorganic phases aims at understanding the chemistry at the interface, and the electronic and morphological properties of the system. This work should be generally applicable to other conjugated polymers and nanostructures, and it contributes to an understanding of organic–inorganic interfaces and structures that may be advantageous to a range of electronic/photonic applications.

Energy level alignment at interfaces is critical for fundamental understanding and optimization of organic photovoltaics (OPV) as band offsets of the donor and acceptor materials largely determine the open circuit voltage (Voc) of the device. Using ultraviolet photoemission spectroscopy (UPS) and inverse photoemission spectroscopy (IPS), we examined the correlation between energy level alignment and photovoltaic properties of a model bilayer hybrid solar cell incorporating electrodeposited polythiophene (e-PT) films on ZnO planar substrates. The electrolyte anion (BF4−, PF6−, ClO4− or CF3SO3−) in the electrodeposition solution was found to have a strong influence on the e-PT film morphology and adhesion, the energy level alignment at the interface, and ultimately the Voc of the photovoltaic devices.