Lead halide perovskite materials have attracted significant attention in the context of photovoltaics and other optoelectronic applications, and recently, research efforts have been directed to nanostructured lead halide perovskites. Collodial nanocrystals (NCs) of cesium lead halides (CsPbX₃, X = Cl, Br, I) exhibit bright photoluminescence, with emission tunable over the entire visible spectral region. However, previous studies on CsPbX₃ NCs did not address key aspects of their chemistry and photophysics such as surface chemistry and quantitative light absorption. Here, we elaborate on the synthesis of CsPbBr₃ NCs and their surface chemistry. In addition, the intrinsic absorption coefficient was determined experimentally by combining elemental analysis with accurate optical absorption measurements. ¹H solution nuclear magnetic resonance spectroscopy was used to characterize sample purity, elucidate the surface chemistry, and evaluate the influence of purification methods on the surface composition. We find that ligand binding to the NC surface is highly dynamic, and therefore, ligands are easily lost during the isolation and purification procedures. However, when a small amount of both oleic acid and oleylamine is added, the NCs can be purified, maintaining optical, colloidal, and material integrity. In addition, we find that a high amine content in the ligand shell increases the quantum yield due to the improved binding of the carboxylic acid.

Colloidal quantum dots based on lead sulfide (PbS) are very attractive materials for the realization of novel image sensors. They offer low cost synthesis, compatibility with a variety of substrates and processing on large area. The tunable band gap enables selective light detection from the visible wavelengths up to the short-wave-infrared (SWIR). This work describes the roadmap towards the integration of quantum dot photodiodes (QDPD) on top of a Si based CMOS read-out circuit. Photodiodes using an n-p junction architecture are fabricated on Si substrates, showing a dark current of 30 nA/cm2 at -1 V reverse bias, EQE above 20% and specific detectivity above 1012 cm Hz1/2 W.1 at the wavelength of 940 nm. Efficiency is improved by reducing absorption in the top contact through optical design. Furthermore, photolithographic patterning of the thin-film stack is introduced for the first time, showing the feasibility of pixel pitches down to 40 μm, opening the way towards high resolution monolithic infrared imagers and the incorporation of infrared and visible sensitive pixels side by side.