Interfacial Heterojunction Enables High Efficient PbS Quantum Dot Solar Cells

Abstract Colloidal quantum dots (CQDs) are promising optoelectronic materials for solution‐processed thin film optoelectronic devices. However, the large surface area with abundant surface defects of CQDs and trap‐assisted non‐radiative recombination losses at the interface between CQDs and charge‐transport layer limit their optoelectronic performance. To address this issue, an interface heterojunction strategy is proposed to protect the CQDs interface by incorporating a thin layer of polyethyleneimine (PEIE) to suppress trap‐assisted non‐radiative recombination losses. This thin layer not only acts as a protective barrier but also modulates carrier recombination and extraction dynamics by forming heterojunctions at the buried interface between CQDs and charge‐transport layer, thereby enhancing the interface charge extraction efficiency. This enhancement is demonstrated by the shortened lifetime of carrier extraction from 0.72 to 0.46 ps. As a result, the resultant PbS CQD solar cells achieve a power‐conversion‐efficiency (PCE) of 13.4% compared to 12.2% without the heterojunction.