Extraordinary Strong Band‐Edge Absorption in Distorted Chalcogenide Perovskites

Abstract

All existing solar cell materials including hybrid perovskites show rather small absorption coefficient (α) of ≈104 cm−1 in the bandgap (Eg) transition region. The weak band‐edge light absorption is an essential problem, limiting conversion efficiency particularly in a tandem solar cell. Herein, all distorted chalcogenide perovskites (BaZrS3, SrZrS3, BaHfS3, and SrHfS3) are found experimentally to exhibit extraordinary high α exceeding 105 cm−1 near Eg, indicating the highest band‐edge α among all known solar cell materials. The giant absorption in the Eg region, which is consistent with the first principles, arises from the intense p–d interband transition enabled by dense S 3p valence states. For solar cell application, low‐gap BaZrS3 derivatives, Ba(Zr,Ti)S3 and BaZr(S,Se)3, are further synthesized. Among the possible candidates of top‐cell materials, an earth‐abundant and nontoxic Ba(Zr,Ti)S3 alloy shows great potential, reaching a maximum potential efficiency exceeding 38% in a chalcogenide perovskite/crystalline Si tandem architecture.

Ti-Alloying of BaZrS3 Chalcogenide Perovskite for Photovoltaics

“…Our results suggest that Ba(Zr 1– x Ti x )S 3 materials are promising candidates as solar absorbers. A similar work was published recently, 25 showing a band gap reduction of 300 meV for Ba(Zr 0.95 Ti 0.05 )S 3 , although the reported band gap of both BaZrS 3 and the Ti-alloyed one is about 150 meV higher than ours and other published studies. 15 − 17 …”

Discovery of highly polarizable semiconductors BaZrS3 and Ba3Zr2SFilippone1, Zhao2, Niu3 et al. 2020Phys. Rev. Materials191181View full textAdd to dashboardCite

“…The Fröhlich coupling constant α parametrizes the interaction between charge carriers and polar phonons, and the tendency toward polaron formation. We estimate α ≈ 0.8−2 for BaZrS 3 and α ≈ 1 for Ba 3 Zr 2 S 7 , using available data for phonon frequency and electron effective mass [4,18,19]. These are comparable to the range reported for lead halide perovskites (1.5-2.7) and implies that charge carriers may be large polarons [20,21].…”

“…BaZrS 3 is isostructural with GdFeO 3 in the distortedperovskite structure, in space group Pnma [3]. It has a direct band gap of E g = 1.83 eV and strong optical absorption above the band gap [3,4]. Ba 3 Zr 2 S 7 forms in a two-layer Ruddlesden-Popper (RP) structure, in space group P4 2 /mnm [2].…”

Flexible Solar Yarns with 15.7% Power Conversion Efficiency, Based on Electrospun Perovskite Composite Nanofibers

“…Organic-inorganic hybrid perovskite materials (MBX 3 ) have become a focal point of research in the photovoltaic field, as they hit a record PCE of 23.32% and beyond on rigid substrates, [1,2] 18.28% on flexible substrates, [3] and 9.49% for fiber-shaped devices. [4] It has been established that the outstanding performance of perovskite solar cells in comparison with the other counterparts is induced by the low electron-hole binding energy, which is below 50 meV for CH 3 NH 3 PbI 3 and about 150 meV for CH 3 NH 3 PbBr 3 , [5,6] high electron mobility (24 AE 7 cm 2 V À1 s À1 ) and hole mobility (105 AE 35 cm 2 V À1 s À1 ), together with a long diffusion lengths (rising above 175 μm), [7] extended charge carrier lifetime, exceeding 446 ns, [8] rapid interfacial charge transfer ability between the material and the adjacent layers, [9] superior structural defect tolerance and shallow point defects, [10] which are thought to be contributed by the ionic bonds holding together perovskite molecules, [11,12] and strong optical absorption due to s-p antibonding coupling [13] etc.…”