Assessing the Optoelectronic Performance of Halide Perovskite Quantum Dots with Identical Bandgaps: Composition Tuning Versus Quantum Confinement

Halide perovskite quantum dots (QDs) have been considered promising materials for constructing low-cost, high-performing optoelectronics. Tuning their bandgaps can be accomplished through size-dependent quantum confinement or altering chemical compositions. To unravel the differences and similarities between these two approaches, two types of QDs, namely, CsPbI3 and CsPbI2.5Br0.5 QDs, were synthesized with different sizes but with the same bandgap of 1.85 eV. Aberration-corrected scanning transmission electron microscopy reveals extensive structural defects and nonperovskite phase in mixed-halide QDs, correlating with the nonuniform strain distribution. Pressure-dependent photoluminescence (PL) suggests lower structural stability and distinct lattice distortion in mixed-halide QDs. Furthermore, time-resolved PL and transient absorption measurements indicate longer carrier lifetimes in pure-halide QDs. Finally, the CsPbI3 QD solar cell delivered an enhanced power conversion efficiency of 16.1% compared with the mixed-halide counterpart (12.8%). This work provides valuable insights into tailoring quantum confinement and composition engineering strategies for achieving QDs with optimal optoelectronic performance.