Methylammonium Bismuth Iodide as a Lead‐Free, Stable Hybrid Organic–Inorganic Solar Absorber

Abstract

Methylammonium lead halide (MAPbX3 ) perovskites exhibit exceptional carrier transport properties. But their commercial deployment as solar absorbers is currently limited by their intrinsic instability in the presence of humidity and their lead content. Guided by our theoretical predictions, we explored the potential of methylammonium bismuth iodide (MBI) as a solar absorber through detailed materials characterization. We synthesized phase-pure MBI by solution and vapor processing. In contrast to MAPbX3, MBI is air stable, forming a surface layer that does not increase the recombination rate. We found that MBI luminesces at room temperature, with the vapor-processed films exhibiting superior photoluminescence (PL) decay times that are promising for photovoltaic applications. The thermodynamic, electronic, and structural features of MBI that are amenable to these properties are also present in other hybrid ternary bismuth halide compounds. Through MBI, we demonstrate a lead-free and stable alternative to MAPbX3 that has a similar electronic structure and nanosecond lifetimes.

Perovskite-Inspired Photovoltaic Materials: Toward Best Practices in Materials Characterization and Calculations

“…47 Challenges also exist in performing quantum mechanical calculations on some of these materials. These calculations are used to predict the thermodynamically stable crystal structure for a given composition, 21 and are also often used to predict the electronic structure. 27,28,30,31 As suggested by recent literature, these calculations have become a critical component in the search for novel photovoltaic materials.…”

“…27,28,30,31 As suggested by recent literature, these calculations have become a critical component in the search for novel photovoltaic materials. 17,20,21,25,28,30,31,48,49 However, the layered structure and presence of partially-oxidized heavy metal cations in many of these materials necessitate special care when performing these calculations.…”

Strongly Enhanced Photovoltaic Performance and Defect Physics of Air‐Stable Bismuth Oxyiodide (BiOI)

“…[5,9,[11][12][13] Timecorrelated single photon counting (TCSPC) measurements of (CH 3 NH 3 ) 3 Bi 2 I 9 and Cs 2 AgBiBr 6 , among others, have shown that these materials exhibit lifetimes exceeding 1 ns. [11,15,16] This is significant because analysis of established thin-film solar absorbers has shown that materials with minority-carrier lifetimes of 1 ns or above have the potential to reach or exceed 10% efficiency. [17] Many of these bismuth halides and chalcohalides have also demonstrated improved air-stability compared to hybrid lead-halide perovskites.…”

“…[17] Many of these bismuth halides and chalcohalides have also demonstrated improved air-stability compared to hybrid lead-halide perovskites. [11,13,15] However, devices based on these materials have low reported power conversion efficiencies under AM 1.5G illumination, between 0.1 and 1.2%. [1] The short-circuit current densities (J SC , <4 mA cm −2 ) and external quantum efficiencies (EQEs, <60%) have also been poor, [1,18] in spite of efforts to extend the photoconversion range of bismuth halide semiconductors (J SC < 3.4 mA cm −2 , EQE < 25%).…”

“…This is a two orders of magnitude improvement in stability over methylammonium lead iodide. [11] We measured the bandgap of BiOI to be 1.93 eV: The indirect bandgap [31] was taken into account by using an exponent of 0.5 in the vertical axis term on the Tauc plot (Figure 1c, inset). This agreed with the photoluminescence peak centered at 1.9 eV (Figure 1c), red appearance of the films (Figure 1b), and previous reports.…”