Solution Processed Fabrication of Se–Te Alloy Thin Films for Application in PV Devices

Abstract

In this work, we report the first-ever fabrication of solution-processed Se–Te alloy thin films for photovoltaic applications using an amine–thiol solvent system. By controlling the relative quantity of Se and Te in ethylenediamine–ethanethiol (EN–ET) solution mixtures, films with different Se/Te ratios were fabricated at temperatures as low as 200 °C with phase-pure material synthesis and uniform homogenous alloying. These composition variations then successfully demonstrated band gap variation from 1.80 eV for pure Se to 1.18 eV for a film with 60% Se and 40% Te that closely matches the theoretical values calculated from Vegard’s law for these materials. Using the evaporation process, the isolation of chalcogen complexes from the EN–ET solution was performed, which was followed by the addition of foreign solvents like dimethyl sulfoxide, dimethyl formamide, and ethanolamine, which enabled the fabrication of better quality films using the spin coating process, minimizing the porosity and increasing the uniformity of the film. A preliminary device fabricated from these films showed diode characteristics with encouraging photovoltaic performance (a power conversion efficiency of 1.11%) that demands further optimization with film fabrication, selection of device architecture, and detailed defect analysis for this material.

Origin of photovoltaic losses in selenium solar cells with open-circuit voltages approaching 1 V

“…In the search of wide bandgap photoabsorbers that are process compatible for fabrication on lower bandgap photoabsorbers, the elemental p-type semiconductor selenium is experiencing renewed interest. [1][2][3][4][5][6] With a reported direct bandgap between 1.8 and 2.0 eV in its trigonal phase and a range of processing temperatures below its melting point of 220 °C, it is an attractive candidate for a top cell in monolithic tandem photovoltaic devices. 7,8 A power conversion efficiency of 5.0% for a singlejunction selenium cell was achieved in the 1980's.…”

Crystal Growth in Se–Te Chalcogenides: Overview of the Growth/Relaxation/Viscosity Interplay for Bulk Glasses and Thin Films

“…The Se–Te glasses (and other Ge/As/In/Bi/Cu-doped materials based on these matrices) are also important technologically, finding utilization in various applications: infrared optics (fibers, lenses, mirrors, etc. ), 3D memory arrays compatible with CMOS technology of microelectronics and photonics, superconducting wires and tapes, high-performance thermoelectric materials, etc. − Moreover, controlled crystal growth may also allow for the transformation of the amorphous 3D structure into the 2D or 1D crystalline structures for state-of-art technological applications. − In all these applications, the knowledge of the crystal growth kinetics is crucial for their practical employment.…”

Spiers Memorial Lecture: Next generation chalcogenide-based absorbers for thin-film solar cells

“…61 Another direction of current interest relates to tuning of the Se absorber bandgap to lower values, for example by alloying with Te. 63,64 Further, there remains a need to understand and engineer recombination pathways and doping (Fermi level control) in this system.…”