This contribution concerns the effect of the Ag content in wide‐gap AgwCu1‐wIn1‐xGaxSe2 (ACIGS) absorber films and its impact on solar cell performance. First‐principles calculations are conducted, predicting trends in absorber band gap energy (Eg) and band structure across the entire compositional range (w and x). It is revealed that a detrimental negative conduction band offset (CBO) with a CdS buffer can be avoided for all possible absorber band gap values (Eg = 1.0–1.8 eV) by adjusting the Ag alloying level. This opens a new path to reduce interface recombination in wide‐gap chalcopyrite solar cells. Indeed, corresponding samples show a clear increase in open‐circuit voltage (VOC) if a positive CBO is created by sufficient Ag addition. A further extension of the beneficial compositional range (positive CBO at buffer/ACIGS interface) is possible when exchanging CdS with Zn1‐ySnyOz, because of its lower electron affinity (χ). Nevertheless, the experimental results strongly suggest that at present, residual interface recombination still limits the performance of solar cells with optimized CBO, which show an efficiency of up to 15.1% for an absorber band gap of Eg = 1.45 eV.

Chalcogenide perovskites have recently emerged into the spotlight as highly robust, earth abundant, and nontoxic candidates for various energy conversion applications, not least photovoltaics (PV). Now, a serious effort is required to determine if they can emulate the PV performance of the better‐known, part‐organic halide perovskites, in applications such as tandem solar cells. This review summarizes the surprisingly large body of literature pertaining to chalcogenide perovskites, which have been investigated for many years despite only recently being considered for applications. The confusing variety of claims coming from computational materials discovery is clarified, and it is specified which chalcogenide perovskites actually exist and should form the focus of experimental work. The highly interesting optoelectronic and transport properties of the known materials at their current stage of development are summarized, which makes a clear case for investigating them further. The existing synthesis literature is collated, which provides some important and possibly unnoticed clues to experimentalists grappling with these somewhat challenging materials. The authors hope that the highlighting of this information will facilitate further exciting studies, better approaches, and new progress for chalcogenide perovskites.

This contribution evaluates the effect of absorber off‐stoichiometry in wide‐gap (Ag,Cu)(In,Ga)Se2 (ACIGS) solar cells. It is found that ACIGS films show an increased tendency to form ordered vacancy compounds (OVCs) with increasing Ga and Ag contents. Very little tolerance to off‐stoichiometry is detected for absorber compositions giving the desired properties of 1) an optimum bandgap (EG) for a top cell in tandem devices (EG = 1.6–1.7 eV) and at the same time 2) a favorable band alignment with a CdS buffer layer. Herein, massive formation of either In‐ or Ga‐enriched OVC patches is found for group I‐poor ACIGS. As a consequence, carrier transport and charge collection are significantly impeded in corresponding solar cells. The transport barrier appears to be increasing with storage time, questioning the long‐term stability of wide‐gap ACIGS solar cells. Furthermore, the efficiency of samples with very high Ga and Ag contents depends on the voltage sweep direction. It is proposed that the hysteresis behavior is caused by a redistribution of mobile Na ions in the 1:1:2 absorber lattice upon voltage bias. Finally, a broader perspective on OVC formation in the ACIGS system is provided and fundamental limitations for wide‐gap ACIGS solar cells are discussed.

First-principles calculations have become a powerful tool to exclude the Edisonian approach in search of novel 2d materials. However, no universal first-principles criteria to examine the realizability of hypothetical 2d materials have been established in the literature yet. Because of this, and since the calculations are always performed in an artificial simulation environment, one can unintentionally study compounds that do not exist in the experiments. Although investigations of physics and chemistry of unrealizable materials can provide some fundamental knowledge, the discussion of their applications can mislead experimentalists for years and increase the gap between experimental and theoretical research. By analyzing energy convex hull, phonon spectra, and structure evolution during ab initio molecular dynamics simulations for a range of synthesized and recently proposed 2d materials, we construct energy, phonon, and dynamic stability filters which need to be satisfied before proposing novel 2d compounds. We demonstrate the power of the suggested filters for several selected 2d systems, revealing that some of them cannot be ever realized experimentally.

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