stable QDSCs in the past years, and these will be discussed in the following sections both from materials science and device engineering perspectives. Several principal QD materials will be covered separately: lead chalcogenide QDs, lead halide perovskite QDs, and lead-free QDs.

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Light‐harvesting devices made from lead sulfide quantum dot (QD) absorbers are one of the many promising technologies of third‐generation photovoltaics. Their simple, solution‐based fabrication, together with a highly tunable and broad light absorption makes their application in newly developed solar cells, particularly promising. In order to yield devices with reduced voltage and current losses, PbS QDs need to have strategically passivated surfaces, most commonly achieved through lead iodide and bromide passivation. The interdot spacing is then predominantly filled with residual amorphous lead halide species that remain from the ligand exchange, thus hindering efficient charge transport and reducing device stability. Herein, it is demonstrated that a post‐treatment by iodide‐based 2‐phenylethlyammonium salts and intermediate 2D perovskite formation can be used to manage the lead halide excess in the PbS QD active layer. This treatment results in improved device performance and increased shelf‐life stability, demonstrating the importance of interdot spacing management in PbS QD photovoltaics.

Quantum Dot Solar Cells In article number 2202994, Yana Vaynzof and co‐workers report on a strategy to eliminate excess lead halide species from the interdot spacing of lead sulfide quantum dot solar cells. This process significantly enhances the interdot coupling, resulting in improved efficiency and stability of the photovoltaic devices.

cells (SCs), [1,2] photodetectors, [3,4] lightemitting diodes, [5,6] field-effect transistors (FETs), [7,8] and lasers. [9,10] They are processed as colloids with a functionalized surface, making it easy to manipulate their properties on a large scale as a low-cost semiconducting material. [11][12][13] In the case of nanocrystals with a size smaller than twice the exciton Bohr radius, quantum confinement effects determine their electronic structure, making their properties fundamentally different from their bulk counterparts. [14] Properties like a size-dependent bandgap, [15] surface-dictated charge transport, [16] collective phenomena of superstructures, [17,18] and strong infrared absorbance, [19] are all derived from the quantum confinement effect in these nanometer-sized particles, which are usually referred to as quantum dots (QDs).According to their elemental composition, metal sulfide QDs are classified as binary (e.g., PbS, Ag 2 S), ternary (e.g., AgBiS 2 , CuInS 2 ), or quaternary (e.g., Cu 2 ZnSnS 4 , Ag 2 ZnSnS 4 ) semiconductor compounds. Since about 50% of the solar spectrum lies in the infrared region, [20] narrow-bandgap metal sulfide QDs encompassing both the visible and near-infrared parts of the electromagnetic spectrum are of particular interest for solar cell applications. Out of the different metal sulfide QDs, binary PbS QD-based SCs have gathered the most attention due to their high performance, facile and low-cost synthesis and processing, and encouraging possibilities for large-scale fabrication. Recently, a record power conversion efficiency (PCE) of 15.45% has been achieved for PbS QD SCs based on extensive device engineering with optimized extraction layers. [21] The latest advances for these types of devices are focused on either the optimization of the extraction layers or the improvement of interdot coupling. [22][23][24] Heavy metal-free sulfide-based quantum dots have recently attracted significant attention as a more environmentallyfriendly alternative to PbS. In particular, ternary AgBiS 2 QDs are a promising candidate as low-toxicity absorber material in photovoltaic cells. [25] AgBiS 2 QDs exhibit ideal properties for photovoltaics with a bandgap of ≈1-1.1 eV, very high absorption coefficient, and sufficiently good stability. [26] As a result of improving device structure and synthetic approaches, solarThe synthesis of metal sulfide nanocrystals is a crucial step in the fabrication of quantum dot (QD) photovoltaics. Control over the QD size during synthesis allows for precise tuning of their optical and electronic properties, making them an appealing choice for electronic applications. This flexibility has led to the implementation of QDs in both highly-efficient single junction solar cells and other optoelectronic devices including photodetectors and transistors. Most commonly, metal sulfide QDs are synthesized using the hot-injection method utilizing a toxic, and air-and moisture-sensitive sulfur source: bis(trimethylsilyl) sulfide ((TMS) 2 S). Here, bis(stearoyl) sulfide (...