Na-Mediated Stoichiometry Control of FeS₂ Thin Films: Suppression of Nanoscale S-Deficiency and Improvement of Photoresponse

Abstract

Control of the constituent phase and stoichiometry of iron pyrite (FeS2) is a prerequisite for high-performance photovoltaic devices based on this material. If the pyrite contains sulfur-deficiency-related secondary phases which have a metallic character and a high possibility of coexistence in pyrite films, then significant carrier recombination is expected. In this work, the beneficial role of Na in suppressing the formation of nanoscale or amorphous sulfur-deficient secondary phases is reported with experimental evidence, leading to a higher phase purity for solution-processed pyrite films. The potential reduction of charge recombination via these metallic secondary phases results in significant improvements in both the photopotential and photocurrent intensity of Na-modified pyrite films compared with reference samples.

Fabrication of Iron Pyrite Thin Films and Photovoltaic Devices by Sulfurization in Electrodeposition Method

“…The iron pyrite film is flat and dense. The surface morphology of the film is comparable to that prepared by spin coating [15,29]. EDX, which is similar to the guess of de las Heras, C. et al [30].…”

“…The iron pyrite film is flat and dense. The surface morphology of the film is comparable to that prepared by spin coating [15,29]. As we all know, the conductive type of absorber layer is of great importance to constructing a device.…”

“…The spectra of the iron pyrite film are consistent with that of the purchased iron pyrite powder. Three Raman peaks at approximately 339 cm −1 , 374 cm −1 , and 426 cm −1 originate from iron pyrite and correspond to the S 2 libration, in-phase stretch, and coupled libration/stretch vibrational modes, respectively [15,[25][26][27], which demonstrates that it is a pure iron pyrite film. The results clearly manifest the advantage of sulfurization sintering for the preparation of FeS 2 thin film as compared with the report without sulfurization in the ECD method [17,23].…”

“…However, its development and application have been restricted for decades [5], owing to sulfur vacancies [6], undesired doping [7], surface conduction [8], and so on. So far, the record power conversion efficiency (PCE) of FeS 2 -based solar cells is 2.8% [9][10][11][12][13][14][15]. Therefore, extensive investigation on FeS 2 is still needed, including material synthesis, defect properties, and device physics.…”

Observation of an Internal p–n Junction in Pyrite FeS2 Single Crystals: Potential Origin of the Low Open Circuit Voltage in Pyrite Solar Cells

“…2,4,[6][7][8][9] While many hypotheses have emerged, a definitive explanation remains elusive, despite substantial ongoing interest in pyrite. 7,[9][10][11][12][13][14][15] Recent progress in understanding electronic transport in high quality pyrite single crystals, however, has provided perhaps the strongest clues to date. 9,16 Specifically, transport measurements on high-purity unintentionally-doped n-type pyrite single crystals have recently established a 1-3-nm-thick conductive surface layer.…”