Copper indium diselenide (CuInSe2) is a prototype ternary compound and group I–III–VI semiconductor with useful optoelectronic properties. CuInSe2 nanocrystals have been of significant interest because of their size-tunable optical properties and lack of toxic heavy metals. Because of the particular vacancy and antisite substitutional point defects in CuInSe2, large stoichiometric deviations can be tolerated, sometimes leading to the so-called ordered vacancy compounds (OVCs). Here, we use Raman spectroscopy of oleylamine-capped CuInSe2 nanocrystals and ab initio lattice dynamics modeling to study the concentration and arrangements of (2vCu – + InCu 2+) defect pairs in the nanocrystals. The nanocrystals have randomly distributed defect pairs that become mobile under light excitation and accumulate, as in OVCs, along the [100] direction. Because the high concentration of vacancies in CuInSe2 nanocrystals is compensated by InCu 2+ antisite defects, these nanocrystals do not exhibit an optical plasmon resonance like many other copper chalcogenide nanocrystals. Annealing the nanocrystals at a high temperature (600 °C) was found to significantly reduce the defect concentration.

Copper indium diselenide (CuInSe 2 ) nanocrystals are a prototypical I−III−VI semiconductor quantum dot material, typically synthesized in oleylamine (OLAm) as a solvent and capping ligand, often with the addition of diphenylphosphine (DPP) to improve the reaction yield. Using 1 H nuclear magnetic resonance spectroscopy, we study the association of OLAm and DPP on CuInSe 2 nanocrystals and find that they both behave as tightly bonded L-type ligands. There is no observable desorption of OLAm or DPP when a toluene-d 8 dispersion is heated to 100 °C, and no ligand exchange occurs when the nanocrystals are exposed to other L-type species like trioctylphosphine (TOP) or octadecanethiol (ODT), which can bind as either X-type or L-type. Molecular iodine (I 2 ), however, is found to readily displace both OLAm and DPP from the nanocrystal surface and facilitate efficient and complete ligand exchange with either TOP or ODT and appears to behave as a Lewis acid Z-type ligand. We also find that the X-type ligand, stearic acid, does not bond to the CuInSe 2 nanocrystals under any circumstances.

Methylammonium lead iodide (CH 3 NH 3 PbI 3 , MAPI) is a high-performance solar cell material but lacks stability in the presence of humidity. Addition of a few percent bismuth (Bi) as a trivalent cation substitute for Pb (i.e., MAP(Bi)I) leads to enhanced stability under high (90%) relative humidity (RH). At moderate humidity (60% RH), however, MAP(Bi)I degrades more rapidly than MAPI. Bi incorporation into MAPI either stabilizes or destabilizes the two hydration products, MAPI•H 2 O and PbI 2 , depending on the amount of humidity in the environment.

The incorporation of monovalent silver (Ag + ) cations into methylammonium lead bromide (CH 3 NH 3 PbBr 3 ) perovskite films leads to a strongly preferred (001) crystallographic orientation on a wide variety of substrates, ranging from glass to mesoporous TiO 2 . CH 3 NH 3 PbBr 3 films deposited without Ag + exhibit only a weakly preferred (011) orientation. Compositional maps and depth profiles from time-of-flight secondary ion mass spectrometry (TOF-SIMS) reveal Ag + segregated to grain boundaries and interfaces. In photovoltaic devices (PVs), addition of Ag + to MAPBr films resulted in poorer device performance, most likely because of the observed Ag + segregation in the films.

There has been significant interest in I–III–VI2 nanocrystals for photonic and optoelectronic applications, especially solar cells. CuInSe2 nanocrystals have been studied extensively as model materials for this class of compounds. By incorporation of Ga to make CuIn x Ga1–x Se2 (CIGSe), the optical gap can be tuned by composition as well as size for higher efficiency solar cells or other applications. The synthesis of CIGSe nanocrystals, however, has not been studied in much detail. It turns out that the addition of Ga to the typical arrested precipitation reactions for CuInSe2 nanocrystals in oleylamine (OLAm) leads to very slow particle nucleation and growth rates. In order to achieve consistent morphology, reaction yield, and Ga incorporation, a lengthy (∼24 h) low temperature incubation step is needed. Under these slow growth conditions, the crystal structure of the CIGSe nanocrystals is cubic. By addition of diphenyl­phosphine (DPP) to the reactions, the nucleation and growth rates are significantly increased; however, this leads to CIGSe (and CuGaSe2) nanocrystals with wurtzite phase. In contrast, CuInSe2 nanocrystals made under similar fast-growth conditions are always cubic.