Decoupling the Impact of Deep‐Trap and Band‐Tail States on PbS Quantum Dot Photodetectors via Alkylamine Engineering

ABSTRACT Halide‐capped PbS colloidal quantum dots (CQDs) prepared via solution‐phase ligand exchange (SPLE) are promising materials for next‐generation optoelectronic devices owing to their effective surface passivation. Nevertheless, deep traps and band‐tail states in CQD solids are often intertwined, obscuring individual impacts on device performance. Here, we introduce two alkylamines, pentylamine (PA) and hexylamine (HA), as additives in a butylamine‐based cosolvent system to decouple these electronic defects. The HA additive significantly suppresses deep trap states by improving halide passivation and directly coordinating with Pb on the CQD surface, whereas the PA additive promotes structural ordering and thus reduces band‐tail states in CQD solids due to the formation of a 2D layered structure through its preferential interactions with the halide matrix. Incorporating the HA additive enables PbS CQD photodetectors (PDs) in zero‐bias photovoltaic mode to achieve a remarkable responsivity of 0.76 A/W and an external quantum efficiency of 72% in the short‐wave infrared (SWIR) region. Thus, device performance is dominated by deep traps at the CQD surface and interfacial defects in the device architecture, providing insights for high‐performance CQD optoelectronic devices.