The performance and operational stability of perovskite-based devices heavily rely on the interfacial properties between the photoactive perovskite layer and charge transport layers. Understanding the theoretical relationship between surface/interface dipoles and surface energetics is crucial for scientific understanding and practical applications. In this study, a method is applied that bridges classical electromagnetism and modern atomistic approaches. The impact of dipolar ligand molecules functionalizing the FASnI(3) perovskite surface is investigated, with inspection of the interplay between surface dipole, charge transfer, and local strain effect, and corresponding shifts in the valence level. The results reveal that the contribution of individual molecular entities to surface dipoles and electric susceptibilities follows an essentially additive behavior. The influence of F doping usually used to mitigate Sn oxidation in Sn-based layer for photovoltaic applications, is also discussed. Furthermore, the findings are compared with predictions from classical approaches employing a capacitor model that links the induced vacuum level shift and the molecular dipole moment. The insights gained from the study provide theoretical guidelines for fine-tuning the work functions of materials, thus enabling effective interfacial engineering in this class of semiconductors.

Design of efficient solar energy-conversion materials has attracted much interest in the last few decades. Among these materials, copper-based semiconducting chalcogenides have been employed as alternatives for copper indium gallium selenide thin-film solar cells due to their low toxicity and earth-abundant absorber components. In the present manuscript, structural, electronic, quantum theory of atoms in molecules (QTAIM) topological, and optical properties of ternary chalcogenide CuSbS2, Cu3SbS3, and Cu3SbS4 have been investigated using the full potential linear augmented plane wave method. An indirect band gap is observed for CuSbS2 with Eg = 1.18 eV and a direct band gap is found for Cu3SbS3, and Cu3SbS4 with Eg = 1.28 and 1.0 eV, respectively. The valence band maximum of CuSbS2, Cu3SbS3, and Cu3SbS4 are mainly predominated by a strong Cu-3d and S-3p orbitals hybridization. The conduction band of CuSbS2 and Cu3SbS3 are mainly characterized by Sb-5p orbital and S-3p orbital mixing. However, conduction band of Cu3SbS4 is dominated by the mixing of Sb-5s and S-3p orbitals. It is found that the Cu-S and Sb-S bonds lie in the transit closed-shell zone, between the typical ionic and covalent bonds, the Cu-S bonds being more ionic in nature and the Sb-S bonds being more covalent. The optical properties of CuSbS2, Cu3SbS3, and Cu3SbS4 in terms of absorption coefficient, extinction coefficient, refractive index, and reflectivity have been investigated. It is found that Cu3SbS4 is probably less suitable for optical application than CuSbS2 and Cu3SbS3 as the chemical bonds in Cu3SbS4 are seemingly less polarizable, as assumed from the QTAIM analysis, which seems to be correlated with a lower absorption coefficient.

Metal halide perovskites have recently emerged as one of the most promising classes of semiconductors for various applications, especially in the field of optoelectronics. Lead-based halide perovskite materials, virtually unexploited for decades, have become prominent candidates due to their unique and intrinsic physicochemical and optical properties. Current challenges faced by the scientific community to capitalize on the properties of Pb-based perovskites are mainly associated with environmental concerns due to the toxicity of Pb and their poor stability. Under this context, over recent years, a number of new Pb-free halide perovskite (and perovskite-like) semiconductor classes have been introduced. This Perspective reviews recent developments in Pb-free halide perovskites, which specifically target their application in solar cells, light-emitting devices, and photocatalysts. Each type of Pb-free material is paired with a specific optoelectronic application, and the latest record performances are reported. Although these materials do not yet exhibit as attractive intrinsic optoelectronic properties as the Pb-based halide perovskites, their potential as alternatives for well-suited applications is discussed.

This paper reports a Density Functional Theory (DFT) investigation of the electron density and optoelectronic properties of two-dimensional (2D) MX2 (M = Mo, W and X = S, Se, Te) subjected to biaxial strains. Upon strains ranging from −4% (compressive strain) to +4% (tensile strain), MX2 bilayers keep the same bandgap type but undergo a non-symmetrical evolution of bandgap energies and corresponding effective masses of charge carriers (m*). Despite a consistency regarding the electronic properties of Mo- and WX2 for a given X, the strain-induced bandgap shrinkage and m* lowering are strong enough to alter the strain-free sequence MTe2, MSe2, MS2, thus tailoring the photovoltaic properties, which are found to be direction dependent. Based on the quantum theory of atoms in molecules, the bond degree (BD) at the bond critical points was determined. Under strain, the X-X BD decreases linearly as X atomic number increases. However, the kinetic energy per electron G/ρ at the bond critical point is independent of strains with the lowest values for X = Te, which can be related to the highest polarizability evidenced from the dielectric properties. A cubic relationship between the absolute BD summation of M-X and X-X bonds and the static relative permittivity was observed. The dominant position of X-X bond participating in this cubic relationship in the absence of strain was substantially reinforced in the presence of strain, yielding the leading role of the X-X bond instead of the M-X one in the photovoltaic response of 2D MX2 material.

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Heterostructures based on a CuInSe2 absorber with an AlP buffer have a 12 meV conduction band offset and achieved 27.39% of conversion efficiency.

Two-dimensional MX (M = Ga, In; X = S, Se, Te) homo- and heterostructures are of interest in electronics and optoelectronics. Structural, electronic and optical properties of bulk and layered MX and GaX/InX heterostructures have been investigated comprehensively using density functional theory (DFT) calculations. Based on the quantum theory of atoms in molecules, topological analyses of bond degree (BD), bond length (BL) and bond angle (BA) have been detailed for interpreting interatomic interactions, hence the structure–property relationship. The X–X BD correlates linearly with the ratio of local potential and kinetic energy, and decreases as X goes from S to Te. For van der Waals (vdW) homo- and heterostructures of GaX and InX, a cubic relationship between microscopic interatomic interaction and macroscopic electromagnetic behavior has been established firstly relating to weighted absolute BD summation and static dielectric constant. A decisive role of vdW interaction in layer-dependent properties has been identified. The GaX/InX heterostructures have bandgaps in the range 0.23–1.49 eV, absorption coefficients over 10−5 cm−1 and maximum conversion efficiency over 27%. Under strain, discordant BD evolutions are responsible for the exclusively distributed electrons and holes in sublayers of GaX/InX. Meanwhile, the interlayer BA adjustment with lattice mismatch explains the constraint-free lattice of the vdW heterostructure.

Two-dimensional MX2 (M = Mo, W; X = S, Se, Te) homo- and heterostructures have attracted extensive attention in electronics and optoelectronics due to their unique structures and properties. In this work, the layer-dependent electronic and optical properties have been studied by varying layer thickness and stacking order. Based on the quantum theory of atoms in molecules, topological analyses on interatomic interactions of layered MX2 and WX2/MoX2, including bond degree (BD), bond length (BL), and bond angle (BA), have been detailed to probe structure-property relationships. Results show that M-X and X-X bonds are strengthened and weakened in layered MX2 compared to the counterparts in bulks. X-X and M-Se/Te are weakened at compressive strain while strengthened at tensile strain and are more responsive to the former than the latter. Discordant BD variation of individual parts of WX2/MoX2 accounts for exclusively distributed electrons and holes, yielding type-II band offsets. X-X BL correlates positively to binding energy (Eb), while X-X BA correlates negatively to lattice mismatch (lm). The resulting interlayer distance limitation evidences constraint-free lattice of vdW structure. Finally, the connection between microscopic interatomic interaction and macroscopic electromagnetic behavior has been quantified firstly by a cubic equation relating to weighted BD summation and static dielectric constant.

Among the CuIn1−xAlxSe2 alloys, that with x = 0.25 is the optimal one in terms of band gap and conversion efficiency. Its absorption coefficient is highly modified under biaxial strains that occur in thin films.