Gold-Based Double Perovskite-Related Polymorphs: Low Dimensional with an Ultranarrow Bandgap

Abstract

Lead-free halide double perovskites (LFDPs) arouse great interest as environmentally friendly substitutes to the state-of-the-art lead halide perovskites. However, most halide LFDPs feature large bandgaps that afford weak visible-light absorption. Herein, we synthesized and systemically studied the single-crystallographic, physical−chemical, band structural, and electronic properties of a series of multidimensional Au-based lead-free hybrid polymorphs, 7,8,9). Among these twodimensional (2D) perovskite-related and zero-dimensional nonperovskite polymorphs, we found an abnormal variation of structural dimensionality with increasing the size of A-site cations. These polymorphs displayed ultrabroad absorption ranges (200− 1300 nm) and tunable low indirect bandgaps (0.93−1.18 eV). Combined single-crystallography and Hall effect measurements demonstrate that the I 3 − conduces to the formation of 2D perovskite structures related by connecting with the (AuI 4 ) − sheets and also the charge transport properties. Consequently, [NH 3 (CH 2 ) 5 NH 3 ][(AuI 4 )I 3 ] and [NH 3 (CH 2 ) 8 NH 3 ] 2 [(AuI 4 )(AuI 2 )(I 3 ) 2 ] showed high spectroscopic limited maximum efficiencies of 28.4 and 20.5%, respectively, with a film thickness of 500 nm. Our findings bring the Au-based polymorphs to the forefront of study on lead-free low-bandgap perovskites for optoelectronics and reveal the unique rule of dimensionality engineering in such materials.

Gold Polyiodide Hybrid Perovskite Solar Cells

“…The compounds were characterized optically through diffuse reflectance spectroscopy and transformation of the obtained data by applying the Kubelka−Munk function 29 yielded optical bandgaps of 1.40 and 1.25 eV, respectively (Figure 2c, d). These narrow bandgaps are akin to some recently reported gold perovskitetype compounds 18 and indicate suitability for photovoltaics. Photoluminescence spectroscopy is a valuable tool to further assess the optoelectronic properties of new materials and was therefore used to evaluate 1 and 2.…”

“…Recently, some gold halide hybrid perovskites have drawn attention in the perovskite field; however, no reports of the photovoltaic performance have been made. − Yet, the chemical diversity of gold perovskites is vast and this class of compounds is largely unexplored. Gold halide hybrid perovskites are typically composed of a cation and either one, or a mixture, of the anions Au I X 2 and Au III X 4.…”

Challenges and Progress in Lead‐Free Halide Double Perovskite Solar Cells

“…[ 69 ] Changing Cs + to a larger organic cation MA + , the crystal structure changed to a Ruddlesden–Popper (R–P)‐type 2D structure. [ 72 ] These 2D organic−inorganic gold HDPs MA 2 Au 2 X 6 also exhibit small bandgaps of 1.02 eV for MA 2 Au 2 I 6 crystals, 1.22 eV for MA 2 Au 2 I 6 films, and 1.38 eV for MA 2 Au 2 Br 6 films (Figure 8d). [ 73 ] .…”

“…[82] An exceptional finding is that the Cs 2 AgBiI 6 nanocrystals synthesized by the anion exchange method could be stable for a short time. [51] Actullay, there are also some HDPs with low bandgaps, including Cs 2 Au 2 I 6 (1.06, 1.31 eV), [69,83] MA 2 Au 2 I 6 (1.02, 1.22 eV), [72,73] MA 2 Au 2 Br 6 (1.38 eV), [73] Cs 2 AgSbBr 6 (1.64 eV), [53] Cs 2 AgFeCl 6 (1.62 eV), [64] and Cs 2 AgTlBr 6 (0.95 eV) [65] ; however, all these materials have not yet been successfully used in efficient solar cell devices due to other challenges, which will be discussed later.…”

Enabling Fast Photoresponse in Near‐Infrared Organic Phototransistors by Manipulating Minority Charge Trapping and Recombination

“…[10,17,18] It is validated that BHJ active layer has the advantage of high exciton dissociation efficiency in many organic devices including solar cells, photodiodes, and OPTs. [24][25][26][27][28][29][30][31] However, the intrinsic response speed in OPTs is usually slow, down to several seconds level, due to the relatively low charge mobility and long trap lifetime in disordered organic materials with partially ordered packaging of the molecules than those in the ordered materials with rigid crystal structures such as single crystal materials. [22,32] Shortening the channel length of the OPT can reduce the transit time of the carriers to reduce the response time.…”