Progress and applications of (Cu–)Ag–Bi–I semiconductors, and their derivatives, as next-generation lead-free materials for photovoltaics, detectors and memristors

Abstract

The search for efficient but inexpensive photovoltaics over the past decade has been disrupted by the advent of lead-halide perovskite solar cells. Despite impressive rises in performance, the toxicity and stability concerns of these materials have prompted a broad, interdisciplinary community across the world to search for lead-free and stable alternatives. A set of such materials that have recently gained attention are semiconductors in the CuI–AgI–BiI3 phase space and their derivatives. These materials include ternary silver bismuth iodide compounds (Ag aBi bI a+3 b), ternary copper bismuth iodide Cu–Bi–I compounds and quaternary Cu–Ag–Bi–I materials, as well as analogues with Sb substituted into the Bi site and Br into the I site. These compounds are comprised of a cubic close-packed sub-lattice of I, with Ag and Bi occupying octahedral holes, while Cu occupies tetrahedral holes. The octahedral motifs adopted by these compounds are either spinel, CdCl2-type, or NaVO2-type. NaVO2-type Ag aBi bI a+3 b compounds are also known as rudorffites. Many of these compounds have thus far demonstrated improved stability and reduced toxicity compared to halide perovskites, along with stable bandgaps in the 1.6–1.9 eV range, making them highly promising for energy harvesting and detection applications. This review begins by discussing the progress in the development of these semiconductors over the past few years, focusing on their optoelectronic properties and process–property–structure relationships. Next, we discuss the progress in developing Ag–Bi–I and Cu–Bi–I compounds for solar cells, indoor photovoltaics, photodetectors, radiation detectors and memristors. We conclude with a discussion of the critical fundamental questions that need to be addressed to push this area forward, and how the learnings from the wider metal-halide semiconductor field can inform future directions.

Ternary Complexes of BiI3/CuI and SbI3/CuI with Tetrahydrothiophene

“…Thus, there has been increasing push toward lead-free photovoltaic materials . The group 15 metal Bi­(III) and Sb­(III) halides can be combined with various M­(I) or alkylammonium ions to form complex perovskites, such as Cs 3 Bi 2 X 9 − and “elpasolites,” such as Cs 2 AgBiX 6 . − Metals such as Ag­(I) and Cu­(I) have been shown to reduce bandgaps. ,,,− In fact, the simple double salts AgBiI 4 , AgSbI 4 , and CuBiI 4 are themselves modest bandgap semiconductors. − …”

Role of Organic HTLs in Pushing Ag3BiI6 Solar Cells to New Heights by Combining Experiment and Simulation: Achieving Maximum Efficiency

“…In the context of photovoltaics, searching for Bi-based (stable) solar cells is crucial for a number of purposes. 1,2 First, compared to traditional lead halide perovskites, their composition is leadfree, resolving toxicological issues and opening the door for sustainable solar solutions. 3 Moreover, Bi-based materials show better stability with increased resistance against moisture, exposure to light, and heat degradation.…”

“…Fossil fuels have emerged as primarily responsible for meeting the 21st century’s rapidly increasing energy needs, which has resulted in environmental deterioration and an unsettling escalation of the greenhouse effect. In the context of photovoltaics, searching for Bi-based (stable) solar cells is crucial for a number of purposes. , First, compared to traditional lead halide perovskites, their composition is lead-free, resolving toxicological issues and opening the door for sustainable solar solutions . Moreover, Bi-based materials show better stability with increased resistance against moisture, exposure to light, and heat degradation .…”