Photovoltaic Cu₃PS₄ Films via a Combinatorial Synthesis Platform Dedicated to Multi-Anion Semiconductors

Inorganic phosphosulfides – materials containing phosphorus, sulfur, and at least one metal – are a vast and chemically-versatile family of materials. Since metal phosphides and metal sulfides are among the highest-performing optoelectronic semiconductors, it seems reasonable to consider the phosphosulfide family as a potential pool of materials for solar cells, photoelectrochemical cells, and light-emitting diodes. Nevertheless, phosphosulfide semiconductors have very rarely been characterized with these applications in mind.<br/>Only 258 out of over 320,000 chemically plausible phosphosulfides (up to quaternaries) have been synthesized in some form, and just a handful of them have been optoelectronically characterized. Thus, there is significant opportunity for new discoveries, but conventional synthesis approaches would be inefficient and tedious.<br/>In the first part of this contribution, we will present our unique suite of high-throughput thin-film deposition tools dedicated to phosphosulfides and other sulfur-containing multi-anion semiconductors. The main high-throughput synthesis method we use for this project is based on reactive sputtering to generate combinatorial material libraries with two perpendicular gradients. The first gradient goes from sulfur rich to phosphorus rich while the second gradient goes from metal A rich to metal B rich, resulting in a variety of different stoichiometries for, e.g., quaternary phosphosulfides. The deposition suite also includes a rapid thermal annealing furnace with access to reactive sources of sulfur and phosphorus, as well as a separate evaporator for incorporating volatile metals. The whole system is glove-box integrated.<br/>In the second part of this contribution, we will show the first experimental results on Cu₃PS₄ films, the first directly deposited phosphosulfide film specifically intended as a PV or PEC absorber.[1–4] The experimental results are complemented by computational studies carried out within our group. The computational track has been of crucial importance for obtaining properties that are difficult to measure experimentally, and for interpreting experimental results. Importantly, we show that the photoluminescence decay time of unoptimized Cu₃PS₄ films is already above 100 ns, demonstrating that phosphosulfides deserve close attention by the PV and PEC research community.<br/><br/>[1] Shi T, Yin W-J, Al-Jassim M and Yan Y 2013 Structural, electronic, and optical properties of Cu 3 -V-VI 4 compound semiconductors <i>Appl. Phys. Lett.</i> <b>103</b> 152105<br/>[2] Itthibenchapong V, Kokenyesi R S, Ritenour A J, Zakharov L N, Boettcher S W, Wager J F and Keszler D A 2013 Earth-abundant Cu-based chalcogenide semiconductors as photovoltaic absorbers <i>J Mater Chem C</i> <b>1</b> 657–62<br/>[3] Foster D H, Jieratum V, Kykyneshi R, Keszler D A and Schneider G 2011 Electronic and optical properties of potential solar absorber Cu3PSe4 <i>Appl. Phys. Lett.</i> <b>99</b> 181903<br/>[4] Yin X, McClary S A, Song Z, Zhao D, Graeser B, Wang C, Shrestha N, Wang X, Chen C, Li C, Subedi K K, Ellingson R J, Tang W, Agrawal R and Yan Y 2019 A Cu 3 PS 4 nanoparticle hole selective layer for efficient inverted perovskite solar cells <i>J. Mater. Chem. A</i> <b>7</b> 4604–10