Surface functionalization of CuInSe₂ and CsPbI₃ nanocrystals : conversion yields, exciton kinetics, and thermal stability

Solar power is a viable solution to the reduction of global dependence on non-renewable resources. Currently, silicon photovoltaic (PV) devices dominate the market. These devices are not only expensive to manufacture but also have a lengthy production process and they emit significant amounts of CO₂ into the atmosphere. Nanocrystal PVs have the potential to significantly lower manufacturing cost while maintaining high efficiencies. However, challenges with nanocrystal’s surface chemistry have impacted their performance. This dissertation examines the surface functionalization effects for copper indium diselenide (CIS) and cesium lead iodide (CsPbI₃) nanocrystals. Specifically, the effects of surface ligands on conversion yields, exciton kinetics, superlattice formation and thermal stability were explored. Using the hot injection synthetic method, nanocrystals were functionalized with organic ligands. The nanocrystals were characterized using various techniques, such as transmission electron microscopy, transient absorption spectroscopy, and small and wide-angle X-ray scattering. It was found that nanocrystals with less surface vacancies demonstrated the highest PV device performances. Additionally, longer lifetimes were discovered for nanocrystals with phosphinic acid ligands. These results are important prerequisites to the fabrication of low cost nanocrystal PV devices. By determining how the ligands affect the optical and electronic properties, the desired characteristics can be engineered and formed into nanoinks that can be deposited onto substrates under ambient conditions; opposed to the traditionally high energy processing.Chemical Engineerin

Uniform selenization of crack-free films of Cu(In,Ga)Se2 nanocrystals

Crack-free films of Cu(In,Ga)Se2 (CIGS) nanocrystals were deposited with uniform thickness (>1 μm) on Mo-coated glass substrates using an ink-based, automated ultrasonic spray process, then selenized and incorporated into photovoltaic devices (PVs). The device performance depended strongly on the homogeneity of the selenized films. Cracks in the spray-deposited films resulted in uneven selenization rates and sintering by creating paths for rapid, uncontrollable selenium (Se) vapor penetration. To make crack-free films, the nanocrystals had to be completely coated with capping ligands in the ink. The selenization rate of crack-free films then depended on the thickness of the nanocrystal layer, the temperature, and duration of Se vapor exposure. Either inadequate or excessive Se exposure leads to poor device performance, generating films that were either partially sintered or exhibited significant accumulation of carbon and selenium. The deposition of uniform nanocrystal films is expected to be important for a variety of electronic and optoelectronic device applications.Fil: Harvey, Taylor B.. Texas A&M University; Estados UnidosFil: Bonafé, Franco Paúl. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Updegrave, Ty. University of Texas at Austin; Estados UnidosFil: Voggu, Vikas Reddy. University of Texas at Austin; Estados UnidosFil: Thomas, Cherrelle. University of Texas at Austin; Estados UnidosFil: Kamarajugadda, Sirish C.. University of Texas at Austin; Estados UnidosFil: Stolle, C. Jackson. University of Texas at Austin; Estados UnidosFil: Pernik, Douglas. University of Texas at Austin; Estados UnidosFil: Du, Jiang. University of Texas at Austin; Estados UnidosFil: Korgel, Brian A.. University of Texas at Austin; Estados Unido

Plastic Microgroove Solar Cells Using CuInSe₂ Nanocrystals

Plastic photovoltaic devices (PVs) were fabricated by spray-depositing copper indium diselenide (CuInSe₂) nanocrystals into micrometer-scale groove features patterned into polyethylene terephthalate (PET) substrates. Each groove has sidewall coatings of Al/CdS and Au and performs as an individual solar cell. These PV groove features can be linked electrically in series to achieve high voltages. For example, cascades of up to 15 grooves have been made with open-circuit voltages of up to 5.8 V. On the basis of the groove geometry, the power conversion efficiencies (PCEs) of the devices reached as high as 2.2%. Using the active area and photovoltaic response of devices determined from light-beam-induced current (LBIC) and photoreflectivity measurements gave PCE values as high as 4.4%