Hybrid solar cells: basic principles and the role of ligands

For the last decade, researchers have attempted to construct photovoltaic (PV) devices using a mixture of inorganic nanoparticles and conjugated polymers. The goal is to construct layers that use the best properties of each material e.g., flexibility from the polymer and high charge mobility from the nanoparticles or blue absorbance from the polymer complementing red absorbance from the nanoparticles. This critical review discusses the main obstacles to efficient hybrid organic/inorganic PV device design in terms of contributions to the external and internal quantum efficiencies. We discuss in particular the role that ligands on the nanoparticles play for mutual solubility and electronic processes at the nanoscale. After a decade of work to control the separation distance between unlike domains and the connectivity between like domains at the nanoscale, hybrid PV device layers are gaining in efficiency, but the goal of using the best properties of two mixed materials is still elusive.