AgBiI₄ as a Lead-Free Solar Absorber with Potential Application in Photovoltaics

Abstract

AgBiI4 powder, crystals, and polycrystalline films were synthesized by sealed tube solid state reactions, chemical vapor transport (CVT), and solution processing, respectively, and their structural, optical and electronic properties are reported. The structure of AgBiI4 is based unambiguously upon a cubic close packed iodide sublattice, but it presents an unusual crystallographic problem: we show that the reported structure, a cubic defect-spinel, cannot be distinguished from a metrically cubic layered structure analogous to CdCl2 using either powder or single crystal X-ray crystallography. In addition, we demonstrate the existence a noncubic CdCl2-type polymorph by isolation of nontwinned single crystals. The indirect optical band gap of AgBiI4 is measured to be 1.63(1) eV, comparable to the indirect band gap of 1.69(1) eV measured for BiI3 and smaller than that reported for other bismuth halides, suggesting that structures with a close-packed iodide sublattice may give narrower band gaps than those with perovskite structures. Band edge states closely resemble those of BiI3; however, the p-type nature of AgBiI4 with low carrier concentration is more similar to MAPbI3 than the n-type BiI3. AgBiI4 shows good stability toward the AM1.5 solar spectrum when kept in a sealed environment and is thermally stable below 90 °C.

High Photon‐to‐Current Conversion in Solar Cells Based on Light‐Absorbing Silver Bismuth Iodide

“…Moreover, BiI 3 shows promising efficiency in solar cells and other bismuth‐halide materials show interesting properties that may be useful in solar cells . A screening of different Ag 1‐3 x Bi 1+ x I4 (0< x <0.19) compounds has previously been performed, indicating that there exist several stable compositions and the structure is not trivial owing to the vacancies in the system …”

“…[29] As creening of different Ag 1-3x Bi 1 + x I4 (0 < x < 0.19) compounds has previously been performed, indicating that there exist several stable compositions and the structure is not trivial owing to the vacancies in the system. [30] Here, solutions with am ixture of silver iodide (AgI) and bismuth iodide (BiI 3 )w ith molar ratio of AgI/BiI 3 = 2:1a nd AgI/ BiI 3 = 1:2w ere used to synthesize materials with differentc rystal structures. These materials were used in as olar cell between TiO 2 ,w hich acts as electron-conducting layer,a nd poly(3-hexylthiophene-2,5-diyl) (P3HT), whichi su sed as holetransportl ayer.T he PCE of the best devices was above 2% under 1000 Wm À2 (1 sun), AM 1.5 Gs imulateds olar illumination.…”

Photovoltaic Rudorffites: Lead‐Free Silver Bismuth Halides Alternative to Hybrid Lead Halide Perovskites

“…Recently,S ansom et al [30] investigated the structure of AgBiI 4 by using single crystal X-ray diffraction (SCXRD) and powder Xray diffraction (PXRD)a nd found that although the structure of AgBiI 4 is based unambiguously upon ac ubic-close-packed iodide sublattice, the cation sublattice can adopt either ac ubic-defect-spinel structure, in whicha ll tetrahedral sites are empty (i.e.,t he rudorffite structure according to the NaVO 2 prototype), or am etrically cubic-layered structure analogues to CdCl 2 .…”

Green fabrication of stable lead-free bismuth based perovskite solar cells using a non-toxic solvent

“…O In contrast to tin-based and binary cation perovskite, antimony and bismuth-based perovskite-like materials are highly stable in ambient atmosphere and possess exceptional optoelectronic properties 25 . These have recently been used as a lead-free absorber in PSCs [25][26][27][28][29][30] . To some extent, antimony shares the less sharp onset of absorption as the tin-based systems.…”