Halide Perovskites: Advanced Photovoltaic Materials Empowered by a Unique Bonding Mechanism

Abstract

Outstanding photovoltaic (PV) materials combine a set of advantageous properties including large optical absorption and high charge carrier mobility, facilitated by small effective masses. Halide perovskites (ABX 3 , where X = I, Br, or Cl) are among the most promising PV materials. Their optoelectronic properties are governed by the BX bond, which is responsible for the pronounced optical absorption and the small effective masses of the charge carriers. These properties are frequently attributed to the ns 2 configuration of the B atom, i.e., Pb 6s 2 or Sn 5s 2 ("lone-pair") states. The analysis of the PV properties in conjunction with a quantum-chemical bond analysis reveals a different scenario. The BX bond differs significantly from ionic, metallic, or conventional 2c2e covalent bonds. Instead it is better regarded as metavalent, since it shares about one p-electron between adjacent atoms. The resulting σ-bond, formally a 2c1e bond, is half-filled, causing pronounced optical absorption. Electron transfer between B and X atoms and lattice distortions open a moderate bandgap resulting in charge carriers with small effective masses. Hence, metavalent bonding explains favorable PV properties of halide perovskites, as summarized in a map for different bond types, which provides a blueprint to design PV materials.

Scaling and Confinement in Ultrathin Chalcogenide Films as Exemplified by GeTe

“…The ET and ES values were robust against the choice of the functional type, as these quantities mostly depended on the valence wave function. [ 51 ]…”

Crystallization Kinetics Control Enabled by a Green Ionic Liquid Additive toward Efficient and Stable Carbon-Based Mesoscopic Perovskite Solar Cells

“…Perovskite solar cells (PSCs) based on organometal halide such as ABX 3 (A = CH 3 NH 3 + and CH­(NH 2 ) 2 + ; B = Pb 2+ and Sn 2+ ; X = I – and Br – ) have been established themselves as the research hotspot among the next-generation photovoltaic technologies, which attract numerous researchers and industrialists worldwide. − During the past decade, due to the extraordinary photoelectric characteristics of perovskite materials as well as the accumulated experiences of organic and dye-sensitized solar cells, the power conversion efficiency (PCE) of PSCs has been rapidly raised from the initial 3.8% to an encouraging certified 25.5%, which is approaching that of the commercialized silicon-based solar cells. − Although the state-of-the-art solution-processed PSCs have achieved an extremely high PCE, practical application of perovskite-based solar energy conversion technology requires further advancements in large-area device demonstration and long-term durability. − …”

Transversal Halide Motion Intensifies Band‐To‐Band Transitions in Halide Perovskites

“…[88] The second finding, that is, that the JDOS rises more rapidly in the 425 K MD than in the static DFT calculation, is particularly interesting because previous work has highlighted that already static HaPs feature a JDOS that is steeper close to the absorption edge when compared to other semiconductors. [53][54][55] Here, we find that the JDOS is intensified in the MD at 425 K compared to the result of the static calculation. Taken together, these findings demonstrate that vibrational features occurring in cubic CsPbBr 3 at 425 K strongly impact the JDOS, and we will therefore investigate which pat-terns in the finite-temperature atomic dynamics are responsible for it.…”