Suppression of Thermally Induced Surface Traps in Colloidal Quantum Dot Solids via Ultrafast Pulsed Light

Thermal annealing (TA) of colloidal quantum dot (CQD) films is considered an important process for recent high‐performing CQD solar cells (SCs) due to its beneficial effects on CQD solids, including enhanced electrical conductivity, denser packing of CQD films, and the removal of organic residues and solvents. However, the conventional TA for CQDs, which requires several minutes, leads to hydroxylation and oxidation on the CQD surface, resulting in the formation of trap states and a subsequent decline in SC performance. To address these challenges, this study introduces a flashlight annealing (FLA) technique that significantly reduces the annealing time to the millisecond scale. Through the FLA approach, it successfully suppressed hydroxylation and oxidation, resulting in decreased trap states within the CQD solids while simultaneously preserving their charge transport properties. As a result, CQD SCs treated with FLA exhibited a notable improvement, achieving an open‐circuit voltage of 0.66 V compared to 0.63 V in TA‐treated devices, leading to an increase in power conversion efficiency from 12.71% to 13.50%. Employing ultrafast flashlight annealing (FLA) on colloidal quantum dot (CQD) solids, in contrast to the traditional thermal annealing method, effectively minimizes hydroxylation and oxidation on the CQD surfaces by shortening the annealing time from minutes to milliseconds. This method decreases trap density, resulting in FLA‐treated photovoltaics exhibiting an enhanced efficiency of 13.5% and an increased open‐circuit voltage of 0.66 V.