(color online) The evolution progress of CQD solar cell architectures. (a) The schematic of Schottky CQD solar cell structure and diagram of energy levels.[93] The schematics and energy band diagrams of (b) planar depleted heterojunction solar cell and (c) bulk heterojunction solar cell.[94] (d) Device architectures and energy bending in ZnO/PbS-TBAI and ZnO/PbS-TBAI/PbS-EDT devices at short-circuit conditions.[95]