This abstract presents a solution-processed photovoltaic device based on the PbS (lead sulfide) colloidal quantum dots (CQDs). A simple fabrication method at room temperature makes the solution-processed photovoltaic devices be a suitable cost effective alternative. In addition to simplicity in the fabrication method, a key advantage of photovoltaic devices based on PbS colloidal quantum dots is the tunability of the absorption spectrum by controlling the size and shape of the PbS quantum dots [1].
The structure of the photovoltaic device is shown in the figure. Active area is composed of a superlattice of doped PbS quantum dots sandwiched between two electric contact layers. The active area makes a Schottky contact with an electrode having low work function such as aluminum on one side and an Ohmic contact with a transparent electrode such as ITO (Indium Tin Oxide) on the other side. Absorbed photons in the active layer generate neutral excitons in the PbS quantum dots, and subsequently charge dissociation takes places in the neutral region due to the internal electric field at the Schottky contact. Photogenerated electrons and holes flow toward the Al and ITO contacts, respectively.
Fabrication process starts with the deposition of doped colloidal PbS quantum dots on an ITO coated glass substrate by a layer by layer (LBL) method in an inert condition at room temperature. The process is followed by aluminum deposition on top by physical vapor deposition. Fabricated photovoltaic device illustrates promising sensitivity to both entire visible and portion of infrared spectrum of sun light. Since both device structure and fabrication process are simple and process can be done in room temperature, fabrication on the flexible substrates is also feasible.

References
[1] C. de Mello Donega, "Synthesis and properties of colloidal heteronanocrystals," Chem. Soc. Rev., vol. 40, pp. 1512–1546, 2011.