One of the current key challenges in solar photovoltaics and solar-driven water splitting is to identify an efficient, stable, and inexpensive material to be used as a high-band gap (1.6-2.0 eV) photabsorber in tandem device configurations. To identify promising candidates that have not been considered before, we have computationally screened 705 compounds with the ABS3 formula (A,B = metals; S = sulfur). Only 15 compounds pass all the screening rounds, which include criteria such as phase stability, suitable band gap, low effective mass, and defect tolerance. The list of 15 compounds includes the previously synthesized materials BaZrS3 and SrZrS3 , as well as a number of other compounds that have not yet been reported experimentally. We have therefore synthesized and characterized a few of such novel ABS3 compounds in thin film form by means of a two-step process. First, sputter deposition of metallic (AB) or oxide (ABO3) precursors; and subsequently, sulfurization of those precursors in H2S gas.
In this contribution, we will show that LaYS3 is a particularly attractive high-band gap photoabsorber. It features a direct band gap of 2.0 eV, which is optimal for a top photoabsorber in tandem water splitting devices . Furthermore, the offset between its band gap and its photoluminescence peak is only 0.1 eV, implying that band tailing problems are not too severe in this first generation of films. The photoluminescence intensity of LaYS3 also compares well to that of high-quality Cu2ZnSnS4 films. We will present the back- and front contact materials targeted for a single-junction LaYS3 solar cell, the corresponding device architecture, and the challenges encountered in our first attempts at fabricating a LaYS3 solar cell. Issues in the synthesis of other novel ABS3 compounds will briefly be mentioned.
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