Quantum size-confined CHNHPbX (X = Br and I) perovskite nanoplatelets with remarkably high photoluminescence quantum yield (up to 90%) were synthesized by ligand-assisted re-precipitation. Thickness-tunability was realized by varying the oleylamine and oleic acid ligand ratio. This method allows tailoring the nanoplatelet thickness by adjusting the number of unit cell monolayers. Broadly tunable emission wavelengths (450-730 nm) are achieved via the pronounced quantum size effect without anion-halide mixing.

Solution‐based perovskite solar cell fabrication typically involves rather complex processing sequences to yield highest performance. While most studies concentrate on the exploration of processing conditions, the purity levels of common perovskite precursor solutions have been investigated and a number of impurities that are critically important toward controlling the crystallization of perovskites are found. In this study, an in‐depth chemical study of the possible impurities formed during CH3NH3I preparation is presented and their relevance on solar cell processing is revealed. A primary consideration is the chemical transformation of hypophosphorous acid, which plays the role of the stabilizer for HI. The detrimental role of the impurities is best demonstrated by comparing perovskite solar cell devices fabricated from impurity‐free precursors versus precursors containing different concentrations of impurities. Most interestingly, it is revealed that a certain concentration of impurities is detrimental to the growth of large‐grained crystals. PbHPO3 nanoparticles, which are formed after hypophosphorous acid transformation, actually cause crystal domain growth through serving as a nucleation center. This study gives valuable insight into the rate determining steps of perovskite crystal growth and further provides the basis for developing reliable and reproducible high‐performance recipes for perovskite solar cell processing.

We present colloidally stable and highly luminescent ZnxCd1–xS:Mn/ZnS core–shell nanocrystals (NCs) as cost-effective light converters for silicon photovoltaic (PV).

Effective engineering of surface ligands in semiconductor nanocrystals can facilitate the electronic interaction between the individual nanocrystals, making them promising for low-cost optoelectronic applications. Here, the use of high purity Cu 2 ZnSnS 4 (CZTS) nanocrystals as the photoactive layer and hole-transporting material is reported in low-temperature solution-processed solar cells. The high purity CZTS nanocrystals are prepared by engineering the surface ligands of CZTS nanocrystals, capped originally with the long-chain organic ligand oleylamine. After ligand removal, CZTS nanocrystals show substantial improvement in photoconductivity and mobility, displaying also an appreciable photoresponse in a simple heterojunction solar cell architecture. More notably, CZTS nanocrystals exhibit excellent holetransporting properties as interface layer in perovskite solar cells, yielding power conversion efficiency (PCE) of 15.4% with excellent fill factor (FF) of 81%. These findings underscore the importance of removing undesired surface ligands in nanocrystalline optoelectronic devices, and demonstrate the great potential of CZTS nanocrystals as both active and passive material for the realization of low-cost efficient solar cells.