A Small‐Molecule “Charge Driver” enables Perovskite Quantum Dot Solar Cells with Efficiency Approaching 13%

Halide perovskite colloidal quantum dots (CQDs) have recently emerged as a promising candidate for CQD photovoltaics due to their superior optoelectronic properties to conventional chalcogenides CQDs. However, the low charge separation efficiency due to quantum confinement still remains a critical obstacle toward higher‐performance perovskite CQD photovoltaics. Available strategies employed in the conventional CQD devices to enhance the carrier separation, such as the design of type‐Ⅱ core–shell structure and versatile surface modification to tune the electronic properties, are still not applicable to the perovskite CQD system owing to the difficulty in modulating surface ligands and structural integrity. Herein, a facile strategy that takes advantage of conjugated small molecules that provide an additional driving force for effective charge separation in perovskite CQD solar cells is developed. The resulting perovskite CQD solar cell shows a power conversion efficiency approaching 13% with an open‐circuit voltage of 1.10 V, short‐circuit current density of 15.4 mA cm^?2, and fill factor of 74.8%, demonstrating the strong potential of this strategy toward achieving high‐performance perovskite CQD solar cells.     

Steric Impediment of Ion Migration Contributes to Improved Operational Stability of Perovskite Solar Cells

The operational instability of perovskite solar cells (PSCs) is known to mainly originate from the migration of ionic species (or charged defects) under a potential gradient. Compositional engineering of the “A” site cation of the ABX₃ perovskite structure has been shown to be an effective route to improve the stability of PSCs. Here, the effect of size-mismatch-induced lattice distortions on the ion migration energetics and operational stability of PSCs is investigated. It is observed that the size mismatch of the mixed “A” site composition films and devices leads to a steric effect to impede the migration pathways of ions to increase the activation energy of ion migration, which is demonstrated through multiple theoretical and experimental evidence. Consequently, the mixed composition devices exhibit significantly improved thermal stability under continuous heating at 85 °C and operational stability under continuous 1 sun illumination, with an extrapolated lifetime of 2011 h, compared to the 222 h of the reference device.