The architecture of colloidal quantum dot solar cells: Materials to devices

The materials chemistry of Colloidal Quantum Dot (CQDs) suspended in solution and processed into films has provided a foundation onto which useful photovoltaic devices can be built. These active materials offer the benefits of solution processing paired with the flexibility of adjustable bandgaps, tailored to suit a particular need. In parallel with these advances, pursuing device geometries that better leverage the available electronic properties of CQD films has borne fruit in further advancing CQD solar cell performance. For active materials such as CQD films where 1/α, where alpha is the absorption coefficient, is of the same order as the free carrier extraction length, external quantum efficiency (EQE) measurements have proved useful in profiling the effectiveness of each nanometer of device thickness at extracting photogenerated carriers. Because CQD films have the added complications of being made of variable-sized constituent material building blocks as well as being deposited from solution, the nature of charge transport through the films can also be size-dependent and matrix dependent.