Lawrence Berkeley National Laboratory

Although ZnO and ZnS are abundant, stable, environmentally benign, their band gap energies (3.44 eV, 3.72 eV) are too large for optimal photovoltaic efficiency. By using band-corrected pseudopotential density-functional theory calculations, we study how the band gap,optical absorption, and carrier localization can be controlled by forming quantum-well like and nanowire-based heterostructures ofZnO/ZnS and ZnO/ZnTe. In the case of ZnO/ZnS core/shell nanowires, which can be synthesized using existing methods, we obtain a band gap of 2.07 eV, which corresponds to a Shockley-Quiesser efficiency limitof 23 percent. Based on these nanowire results, we propose that ZnO/ZnScore/shell nanowires can be used as photovoltaic devices with organic polymer semiconductors as p-channel contacts.