| AVS 60th International Symposium and Exhibition | |
| Energy Frontiers Focus Topic | Monday Sessions |
| Session EN+AS+NS+SS-MoA |
| Session: | Interfacial Challenges in Nanostructured Solar Cells |
| Presenter: | S. Rangan, Rutgers University |
| Authors: | S. Rangan, Rutgers University A. Batarseh, Rutgers University K.P. Chitre, Rutgers University A. Kopecky, Rutgers University E. Galoppini, Rutgers University R.A. Bartynski, Rutgers University |
| Correspondent: | Click to Email |
The problem of energy level alignment at heterointerfaces is central to the issues of charge transport and charge separation in solid state or hybrid photovoltaic devices, as well as in organic electronic and water splitting applications. In most cases, the energy alignment at interfaces is an ad-hoc property of two materials brought into contact, with the relative ionization or affinity energies possibly altered by charge reorganization at the interface, often called the interface dipole. Attempts to alter this ad-hoc energy alignment have employed strategies ranging from modifying bulk properties to intentionally altering charge redistribution at the interface by local doping. Such approaches, however, offer a very limited level of control.
In this work, we demonstrate that it is possible to separate the contributions of ad-hoc interfacial dipoles from a designed oriented dipole in order to finely tune energy alignment at the interface between a chromophore and a wide band gap oxide. The approach employs a chromophore-bridge-anchor molecular architecture where the three components are electronically decoupled. By introducing electron donor (D) and acceptor (A) groups to the bridge, an intramolecular dipole is introduced between the chromophore and the anchor. When a monolayer of such molecules is bonded to a metal oxide surface, the resulting dipole layer establishes a potential difference that shifts the chromophore levels with respect to those of the substrate.
This concept is demonstrated using a chromophore (ZnTPP)-bridge (substituted with an electron donating (NMe2) and electron withdrawing (NO2) groups to create a built-in dipole)-anchor (Isophtalic acid) architecture. Shifts of the chromophore's HOMOs on the order of plus or minus 0.1 eV with respect to the ZnO valence band edge have been observed, without altering the photoabsorption properties of the chromophore or the HOMO-LUMO gap. An important strength of this concept is that it provides a general design applicable to a large number of anchoring functional groups, built-in dipole bridges, and redox-active centers.