Electronic grade and flexible semiconductor film employing oriented attachment of colloidal ligand-free PbS and PbSe nanocrystals at room temperature

Abstract

Electronic grade semiconductor films have been obtained via the sintering of solution processed PbS and PbSe nanocrystals at room temperature. Prior attempts to achieve similar films required the sintering of nanocrystals at higher temperatures (>350 °C), which inhibits the processing of such films on a flexible polymer substrate, and it is also expensive. We reduced the sintering temperature by employing two important strategies: (i) use of ligand-free nanocrystals and (ii) oriented attachment of nanocrystals. Colloidal ligand-free PbS and PbSe nanocrystals were synthesized at 70 °C with high yield (∼70%). However, these nanocrystals start to agglomerate with time in formamide, and upon the removal of the solvation energy, nanocrystals undergo oriented attachment, forming larger elongated crystals. PbS and PbSe nanocrystal films made on both glass and flexible substrates at room temperature exhibit Ohmic behavior with optimum DC conductivities of 0.03 S m(-1) and 0.08 S m(-1), respectively. Mild annealing of the films at 150 °C increases the conductivity values to 1.1 S m(-1) and 137 S m(-1) for PbS and PbSe nanocrystal films, respectively. AC impedance was measured to distinguish the contributions from grain and grain boundaries to the charge transport mechanism. Charge transport properties remain similar after the repeated bending of the film on a flexible polymer substrate. Reasonably high thermoelectric Seebeck coefficients of 600 μV K(-1) and 335 μV K(-1) for PbS and PbSe nanocrystal pellets, respectively, were obtained at room temperature.

Quantum Dots for Photovoltaics: A Tale of Two Materials

“…[120,121] Although a large variety of surface chemistry treatments such as ligands exchanges have been developed to improve the optoelectronic properties of PbX QDs, these approaches may also produce suspended bonds, thus causing high defect density on its surface. [122][123][124] Consequently, PbX QDs usually suffer from relatively high voltage loss and need high-quality surface passivation when applied in solar cells. [125][126][127] Conversely, PVK QDs show a distinctly high defect tolerance.…”

“…a) Progress in the PCE and the accumulated publication numbers of lead‐based QD solar cells since 2010. [ 88–148 ] The data of the number of publications is taken from Scopus ( www.scopus.com). b) Schematic diagram of the material structure of PbX (X = S, Se) (Reproduced with permission.…”

Two-dimensional copper based colloidal nanocrystals: synthesis and applications

“…6,21 In oriented attachment/self-organisation, the energetically under-passivated crystal facets of NCs attach to form a superstructure assembly which further goes through recrystallisation to form larger nanocrystals. [71][72][73] However, the 2D morphology will form when the preferential binding of ligands to the facet perpendicular to the growth facet constricts the assembly in a two-dimensional template. In the oriented attachment driven growth of 2D nanocrystals, Schliehe et al describe an egg tray-like assembly of PbS quantum dots via attachment of (110) facets where the oleic acid bound to the (100) facets formed a bilayer stacking resulting in PbS nanosheets.…”

Nanostructured Lead Sulphide Depositions by AACVD Technique Using Bis(Isobutyldithiophosphinato)Lead(II) Complex as Single Source Precursor and Its Impedance Study

“…Many researchers have investigated the ferroelectric, dielectric and electrical properties of PbS formed by various synthetic techniques. Shanker and coworkers [14] have employed oriented attachment of colloidal ligand-free PbS and studied flexible electronic grade semiconductors. Mild annealing at 150 • C increased the conductivity of PbS nanocrystals.…”