Gradient-Band Alignment Homojunction Perovskite Quantum Dot Solar Cells.

The inorganic perovskite CsPbI that exists in the form of a quantum dot (QD) shows a stable cubic structure, attracting much attention for its application in solar cells. However, too many grain boundaries in the perovskite QD (PQD) layer block the transport of carriers, resulting in the potential loss of solar cells. Herein, we devise a gradient-band alignment (GBA) homojunction, which is constructed from three layers of PQDs with different band-gaps to form a gradient energy alignment. The GBA structure facilitated the charge extraction and increased the carrier diffusion length of the PQD layer because of the additional driving force for the electrons. In addition, the homojunction made from the same substance could minimize the lattice mismatch of the active layer. As a result, the champion solar cell based on the GBA homojunction layer achieved a high open voltage of 1.25 V and a power conversion efficiency (PCE) of 13.2%.