Strain-Engineered PbS Quantum Dot Solar Cells with Suppressed Trap States and Enhanced Performance

Surface strain in quantum dot (QD) films, while not a defect itself, can distort the local lattice environment and promote the formation of electronic trap states, ultimately limiting charge transport and device performance. Here, we introduce a strain-modulation strategy using guanidinium iodide (GAI) to partially disrupt the continuous PbI₂-based ligand shell on PbS QDs. By relaxing the interfacial lattice strain by 53%, strain-induced trap states are suppressed, improving carrier transport in QD films. Solar cells based on these optimized films achieve a power conversion efficiency of 14.2%, compared to 12.5% in control devices. This study underscores the critical role of surface strain as a hidden regulator of electronic quality in QD solids and offers a new avenue for interfacial strain management in solution-processed optoelectronics.