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, CsPbI 3 and CsPbI 2.5 Br 0.5 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 CsPbI 3 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.