Lead sulfide quantum dots (PbS QDs) are promising candidates for high-performance solar cells due to their tunable bandgaps and low-cost solution processing. However, low carrier mobility and numerous surface defects restrict the performance of the fabricated solar cells. Herein, we report the synthesis of novel PbS-perovskite core-shell QDs to solve the low carrier mobility problem of PbS QDs via a facile hot injection method. CsPbI₂Br shell enabled strain-free epitaxial growth on the surface of PbS QDs because of 98% lattice match. Our results demonstrate a significant improvement in the photoluminescence and stability of the synthesized PbS-CsPbI₂Br QDs upon shell formation, attributed to the effective suppression of surface defects by the epitaxial shell of CsPbI₂Br. As a result, the obtained solar cell based on PbS-CsPbI₂Br core-shell QD exhibits a power conversion efficiency (PCE) of 8.43%, two times higher than that of pristine PbS QDs. Overall, the construction of PbS-CsPbI₂Br core-shell structures represent a promising strategy for advancing the performance of PbS QDs-based optoelectronic devices.

Chloride solid electrolytes (SEs) have attracted widespread attention due to their high room-temperature ionic conductivity and excellent cathode compatibility. However, the conventionally selected central metal elements (e.g., In, Y and Ta) are usually rare and heavy, inevitably causing the high cost and high density of the obtained chloride SEs. Here, by choosing abundant and light Mg and Al as central metal elements, we develop a cheap and low density Li_1.2Mg_0.95Al_0.3Cl₄ SE for high active material ratio in all solid state cathode. Partial replacement of Mg²⁺ by Al³⁺ in the framework yields vacancies and lowers the non-lithium metal ions occupancy at Mg/Li co-occupied 16d site, effectively relieving the blocking effects by Mg²⁺ in the pristine spinel Li_2–2xMg_1+xCl₄. Thus, a significantly improved room-temperature conductivity of 3.08 × 10^–4 S·cm^–1 is achieved, two orders of magnitude higher than that of Li_1.2Mg_1.4Cl₄. More attractively, its low density of only 1.98 g·cm^–3 enables low SE mass ratio in cathodes (only 16 wt.%) with still effective electrolyte/cathode contact and lithium-ion conduction inside. When charged to potential of 4.30 V, the as-fabricated Li_1.2Mg_0.95Al_0.3Cl₄-based solid lithium battery with uncoated NCM523 cathode can be cycled for over 100 cycles with a capacity retention of 86.68% at room temperature.