Method for the Solution Deposition of Phase-Pure CoSe₂ as an Efficient Hydrogen Evolution Reaction Electrocatalyst

We demonstrate the ability of a thiol–amine solvent mixture to deposit phase-pure marcasite-type CoSe₂ nanostructured thin films as effective hydrogen evolution reaction (HER) electrocatalysts. Electrodes are readily prepared by spin coating a precursor ink onto highly ordered pyrolytic graphite substrates followed by annealing to 350 °C. The resulting CoSe₂ films have an onset potential for HER of −117 mV vs RHE and Tafel slopes of ca. 60 mV dec^–1. Normalization based on electrochemically active surface area reveals that simple optimization of film thickness, based on the number of layers deposited, leads to electrodes with better surface utilization. Based on the electrocatalytic performance of the solution-processed CoSe₂ presented here (η_10mA/cm² = −272 mV vs RHE), this approach shows promise as a simple method to deposit a wide range of useful dichalcogenide electrocatalysts

Crystal Structure Evolution and Notable Thermal Expansion in Hybrid Perovskites Formamidinium Tin Iodide and Formamidinium Lead Bromide

The temperature-dependent structure evolution of the hybrid halide perovskite compounds, formamidinium tin iodide (FASnI₃, FA⁺ = CH­[NH₂]₂⁺) and formamidinium lead bromide (FAPbBr₃), has been monitored using high-resolution synchrotron X-ray powder diffraction between 300 and 100 K. The data are consistent with a transition from cubic <i>Pm</i>3<i>m</i> (No. 221) to tetragonal <i>P</i>4/<i>mbm</i> (No. 127) for both materials upon cooling; this occurs for FAPbBr₃ between 275 and 250 K, and for FASnI₃ between 250 and 225 K. Upon further cooling, between 150 and 125 K, both materials undergo a transition to an orthorhombic <i>Pnma</i> (No. 62) structure. The transitions are confirmed by calorimetry and dielectric measurements. In the tetragonal regime, the coefficients of volumetric thermal expansion of FASnI₃ and FAPbBr₃ are among the highest recorded for any extended inorganic crystalline solid, reaching 219 ppm K^–1 for FASnI₃ at 225 K. Atomic displacement parameters of all atoms for both materials suggest dynamic motion is occurring in the inorganic sublattice due to the flexibility of the inorganic network and dynamic lone pair stereochemical activity on the <i>B</i>-site. Unusual pseudocubic behavior is displayed in the tetragonal phase of the FAPbBr₃, similar to that previously observed in FAPbI₃

Unraveling the Chemical Nature of the 3D “Hollow” Hybrid Halide Perovskites

The newly introduced class of 3D halide perovskites, termed “hollow” perovskites, has been recently demonstrated as light absorbing semiconductor materials for fabricating lead-free perovskite solar cells with enhanced efficiency and superior stability. Hollow perovskites derive from three-dimensional (3D) <i>AMX</i>₃ perovskites (<i>A</i> = methylammonium (MA), formamidinium (FA); M = Sn, Pb; X = Cl, Br, I), where small molecules such as ethylenediammonium cations (<i>en</i>) can be incorporated as the dication without altering the structure dimensionality. We present in this work the inherent structural properties of the hollow perovskites and expand this class of materials to the Pb-based analogues. Through a combination of physical and spectroscopic methods (XRD, gas pycnometry, ¹H NMR, TGA, SEM/EDX), we have assigned the general formula (A)_1–<i>x</i>­(<i>en</i>)_<i>x</i>­(M)_{1–0.7<i>x</i>}(X)_{3–0.4<i>x</i>} to the hollow perovskites. The incorporation of <i>en</i> in the 3D perovskite structure leads to massive <i>M</i> and <i>X</i> vacancies in the 3D [<i>MX</i>₃] framework, thus the term hollow. The resulting materials are semiconductors with significantly blue-shifted direct band gaps from 1.25 to 1.51 eV for Sn-based perovskites and from 1.53 to 2.1 eV for the Pb-based analogues. The increased structural disorder and hollow nature were validated by single crystal X-ray diffraction analysis as well as pair distribution function (PDF) analysis. Density functional theory (DFT) calculations support the experimental trends and suggest that the observed widening of the band gap is attributed to the massive <i>M</i> and <i>X</i> vacancies, which create a less connected 3D hollow structure. The resulting materials have superior air stability, where in the case of Sn-based hollow perovskites it exceeds two orders of temporal magnitude compared to the conventional full perovskites of MASnI₃ and FASnI₃. The hollow perovskite compounds pose as a new platform of promising light absorbers that can be utilized in single junction or tandem solar cells

Unraveling the Chemical Nature of the 3D “Hollow” Hybrid Halide Perovskites

The newly introduced class of 3D halide perovskites, termed “hollow” perovskites, has been recently demonstrated as light absorbing semiconductor materials for fabricating lead-free perovskite solar cells with enhanced efficiency and superior stability. Hollow perovskites derive from three-dimensional (3D) <i>AMX</i>₃ perovskites (<i>A</i> = methylammonium (MA), formamidinium (FA); M = Sn, Pb; X = Cl, Br, I), where small molecules such as ethylenediammonium cations (<i>en</i>) can be incorporated as the dication without altering the structure dimensionality. We present in this work the inherent structural properties of the hollow perovskites and expand this class of materials to the Pb-based analogues. Through a combination of physical and spectroscopic methods (XRD, gas pycnometry, ¹H NMR, TGA, SEM/EDX), we have assigned the general formula (A)_1–<i>x</i>­(<i>en</i>)_<i>x</i>­(M)_{1–0.7<i>x</i>}(X)_{3–0.4<i>x</i>} to the hollow perovskites. The incorporation of <i>en</i> in the 3D perovskite structure leads to massive <i>M</i> and <i>X</i> vacancies in the 3D [<i>MX</i>₃] framework, thus the term hollow. The resulting materials are semiconductors with significantly blue-shifted direct band gaps from 1.25 to 1.51 eV for Sn-based perovskites and from 1.53 to 2.1 eV for the Pb-based analogues. The increased structural disorder and hollow nature were validated by single crystal X-ray diffraction analysis as well as pair distribution function (PDF) analysis. Density functional theory (DFT) calculations support the experimental trends and suggest that the observed widening of the band gap is attributed to the massive <i>M</i> and <i>X</i> vacancies, which create a less connected 3D hollow structure. The resulting materials have superior air stability, where in the case of Sn-based hollow perovskites it exceeds two orders of temporal magnitude compared to the conventional full perovskites of MASnI₃ and FASnI₃. The hollow perovskite compounds pose as a new platform of promising light absorbers that can be utilized in single junction or tandem solar cells

Unraveling the Chemical Nature of the 3D “Hollow” Hybrid Halide Perovskites

The newly introduced class of 3D halide perovskites, termed “hollow” perovskites, has been recently demonstrated as light absorbing semiconductor materials for fabricating lead-free perovskite solar cells with enhanced efficiency and superior stability. Hollow perovskites derive from three-dimensional (3D) <i>AMX</i>₃ perovskites (<i>A</i> = methylammonium (MA), formamidinium (FA); M = Sn, Pb; X = Cl, Br, I), where small molecules such as ethylenediammonium cations (<i>en</i>) can be incorporated as the dication without altering the structure dimensionality. We present in this work the inherent structural properties of the hollow perovskites and expand this class of materials to the Pb-based analogues. Through a combination of physical and spectroscopic methods (XRD, gas pycnometry, ¹H NMR, TGA, SEM/EDX), we have assigned the general formula (A)_1–<i>x</i>­(<i>en</i>)_<i>x</i>­(M)_{1–0.7<i>x</i>}(X)_{3–0.4<i>x</i>} to the hollow perovskites. The incorporation of <i>en</i> in the 3D perovskite structure leads to massive <i>M</i> and <i>X</i> vacancies in the 3D [<i>MX</i>₃] framework, thus the term hollow. The resulting materials are semiconductors with significantly blue-shifted direct band gaps from 1.25 to 1.51 eV for Sn-based perovskites and from 1.53 to 2.1 eV for the Pb-based analogues. The increased structural disorder and hollow nature were validated by single crystal X-ray diffraction analysis as well as pair distribution function (PDF) analysis. Density functional theory (DFT) calculations support the experimental trends and suggest that the observed widening of the band gap is attributed to the massive <i>M</i> and <i>X</i> vacancies, which create a less connected 3D hollow structure. The resulting materials have superior air stability, where in the case of Sn-based hollow perovskites it exceeds two orders of temporal magnitude compared to the conventional full perovskites of MASnI₃ and FASnI₃. The hollow perovskite compounds pose as a new platform of promising light absorbers that can be utilized in single junction or tandem solar cells

Unraveling the Chemical Nature of the 3D “Hollow” Hybrid Halide Perovskites

The newly introduced class of 3D halide perovskites, termed “hollow” perovskites, has been recently demonstrated as light absorbing semiconductor materials for fabricating lead-free perovskite solar cells with enhanced efficiency and superior stability. Hollow perovskites derive from three-dimensional (3D) <i>AMX</i>₃ perovskites (<i>A</i> = methylammonium (MA), formamidinium (FA); M = Sn, Pb; X = Cl, Br, I), where small molecules such as ethylenediammonium cations (<i>en</i>) can be incorporated as the dication without altering the structure dimensionality. We present in this work the inherent structural properties of the hollow perovskites and expand this class of materials to the Pb-based analogues. Through a combination of physical and spectroscopic methods (XRD, gas pycnometry, ¹H NMR, TGA, SEM/EDX), we have assigned the general formula (A)_1–<i>x</i>­(<i>en</i>)_<i>x</i>­(M)_{1–0.7<i>x</i>}(X)_{3–0.4<i>x</i>} to the hollow perovskites. The incorporation of <i>en</i> in the 3D perovskite structure leads to massive <i>M</i> and <i>X</i> vacancies in the 3D [<i>MX</i>₃] framework, thus the term hollow. The resulting materials are semiconductors with significantly blue-shifted direct band gaps from 1.25 to 1.51 eV for Sn-based perovskites and from 1.53 to 2.1 eV for the Pb-based analogues. The increased structural disorder and hollow nature were validated by single crystal X-ray diffraction analysis as well as pair distribution function (PDF) analysis. Density functional theory (DFT) calculations support the experimental trends and suggest that the observed widening of the band gap is attributed to the massive <i>M</i> and <i>X</i> vacancies, which create a less connected 3D hollow structure. The resulting materials have superior air stability, where in the case of Sn-based hollow perovskites it exceeds two orders of temporal magnitude compared to the conventional full perovskites of MASnI₃ and FASnI₃. The hollow perovskite compounds pose as a new platform of promising light absorbers that can be utilized in single junction or tandem solar cells

Unraveling the Chemical Nature of the 3D “Hollow” Hybrid Halide Perovskites

The newly introduced class of 3D halide perovskites, termed “hollow” perovskites, has been recently demonstrated as light absorbing semiconductor materials for fabricating lead-free perovskite solar cells with enhanced efficiency and superior stability. Hollow perovskites derive from three-dimensional (3D) <i>AMX</i>₃ perovskites (<i>A</i> = methylammonium (MA), formamidinium (FA); M = Sn, Pb; X = Cl, Br, I), where small molecules such as ethylenediammonium cations (<i>en</i>) can be incorporated as the dication without altering the structure dimensionality. We present in this work the inherent structural properties of the hollow perovskites and expand this class of materials to the Pb-based analogues. Through a combination of physical and spectroscopic methods (XRD, gas pycnometry, ¹H NMR, TGA, SEM/EDX), we have assigned the general formula (A)_1–<i>x</i>­(<i>en</i>)_<i>x</i>­(M)_{1–0.7<i>x</i>}(X)_{3–0.4<i>x</i>} to the hollow perovskites. The incorporation of <i>en</i> in the 3D perovskite structure leads to massive <i>M</i> and <i>X</i> vacancies in the 3D [<i>MX</i>₃] framework, thus the term hollow. The resulting materials are semiconductors with significantly blue-shifted direct band gaps from 1.25 to 1.51 eV for Sn-based perovskites and from 1.53 to 2.1 eV for the Pb-based analogues. The increased structural disorder and hollow nature were validated by single crystal X-ray diffraction analysis as well as pair distribution function (PDF) analysis. Density functional theory (DFT) calculations support the experimental trends and suggest that the observed widening of the band gap is attributed to the massive <i>M</i> and <i>X</i> vacancies, which create a less connected 3D hollow structure. The resulting materials have superior air stability, where in the case of Sn-based hollow perovskites it exceeds two orders of temporal magnitude compared to the conventional full perovskites of MASnI₃ and FASnI₃. The hollow perovskite compounds pose as a new platform of promising light absorbers that can be utilized in single junction or tandem solar cells

Unraveling the Chemical Nature of the 3D “Hollow” Hybrid Halide Perovskites

The newly introduced class of 3D halide perovskites, termed “hollow” perovskites, has been recently demonstrated as light absorbing semiconductor materials for fabricating lead-free perovskite solar cells with enhanced efficiency and superior stability. Hollow perovskites derive from three-dimensional (3D) <i>AMX</i>₃ perovskites (<i>A</i> = methylammonium (MA), formamidinium (FA); M = Sn, Pb; X = Cl, Br, I), where small molecules such as ethylenediammonium cations (<i>en</i>) can be incorporated as the dication without altering the structure dimensionality. We present in this work the inherent structural properties of the hollow perovskites and expand this class of materials to the Pb-based analogues. Through a combination of physical and spectroscopic methods (XRD, gas pycnometry, ¹H NMR, TGA, SEM/EDX), we have assigned the general formula (A)_1–<i>x</i>­(<i>en</i>)_<i>x</i>­(M)_{1–0.7<i>x</i>}(X)_{3–0.4<i>x</i>} to the hollow perovskites. The incorporation of <i>en</i> in the 3D perovskite structure leads to massive <i>M</i> and <i>X</i> vacancies in the 3D [<i>MX</i>₃] framework, thus the term hollow. The resulting materials are semiconductors with significantly blue-shifted direct band gaps from 1.25 to 1.51 eV for Sn-based perovskites and from 1.53 to 2.1 eV for the Pb-based analogues. The increased structural disorder and hollow nature were validated by single crystal X-ray diffraction analysis as well as pair distribution function (PDF) analysis. Density functional theory (DFT) calculations support the experimental trends and suggest that the observed widening of the band gap is attributed to the massive <i>M</i> and <i>X</i> vacancies, which create a less connected 3D hollow structure. The resulting materials have superior air stability, where in the case of Sn-based hollow perovskites it exceeds two orders of temporal magnitude compared to the conventional full perovskites of MASnI₃ and FASnI₃. The hollow perovskite compounds pose as a new platform of promising light absorbers that can be utilized in single junction or tandem solar cells

Unraveling the Chemical Nature of the 3D “Hollow” Hybrid Halide Perovskites

The newly introduced class of 3D halide perovskites, termed “hollow” perovskites, has been recently demonstrated as light absorbing semiconductor materials for fabricating lead-free perovskite solar cells with enhanced efficiency and superior stability. Hollow perovskites derive from three-dimensional (3D) <i>AMX</i>₃ perovskites (<i>A</i> = methylammonium (MA), formamidinium (FA); M = Sn, Pb; X = Cl, Br, I), where small molecules such as ethylenediammonium cations (<i>en</i>) can be incorporated as the dication without altering the structure dimensionality. We present in this work the inherent structural properties of the hollow perovskites and expand this class of materials to the Pb-based analogues. Through a combination of physical and spectroscopic methods (XRD, gas pycnometry, ¹H NMR, TGA, SEM/EDX), we have assigned the general formula (A)_1–<i>x</i>­(<i>en</i>)_<i>x</i>­(M)_{1–0.7<i>x</i>}(X)_{3–0.4<i>x</i>} to the hollow perovskites. The incorporation of <i>en</i> in the 3D perovskite structure leads to massive <i>M</i> and <i>X</i> vacancies in the 3D [<i>MX</i>₃] framework, thus the term hollow. The resulting materials are semiconductors with significantly blue-shifted direct band gaps from 1.25 to 1.51 eV for Sn-based perovskites and from 1.53 to 2.1 eV for the Pb-based analogues. The increased structural disorder and hollow nature were validated by single crystal X-ray diffraction analysis as well as pair distribution function (PDF) analysis. Density functional theory (DFT) calculations support the experimental trends and suggest that the observed widening of the band gap is attributed to the massive <i>M</i> and <i>X</i> vacancies, which create a less connected 3D hollow structure. The resulting materials have superior air stability, where in the case of Sn-based hollow perovskites it exceeds two orders of temporal magnitude compared to the conventional full perovskites of MASnI₃ and FASnI₃. The hollow perovskite compounds pose as a new platform of promising light absorbers that can be utilized in single junction or tandem solar cells

Unraveling the Chemical Nature of the 3D “Hollow” Hybrid Halide Perovskites

The newly introduced class of 3D halide perovskites, termed “hollow” perovskites, has been recently demonstrated as light absorbing semiconductor materials for fabricating lead-free perovskite solar cells with enhanced efficiency and superior stability. Hollow perovskites derive from three-dimensional (3D) <i>AMX</i>₃ perovskites (<i>A</i> = methylammonium (MA), formamidinium (FA); M = Sn, Pb; X = Cl, Br, I), where small molecules such as ethylenediammonium cations (<i>en</i>) can be incorporated as the dication without altering the structure dimensionality. We present in this work the inherent structural properties of the hollow perovskites and expand this class of materials to the Pb-based analogues. Through a combination of physical and spectroscopic methods (XRD, gas pycnometry, ¹H NMR, TGA, SEM/EDX), we have assigned the general formula (A)_1–<i>x</i>­(<i>en</i>)_<i>x</i>­(M)_{1–0.7<i>x</i>}(X)_{3–0.4<i>x</i>} to the hollow perovskites. The incorporation of <i>en</i> in the 3D perovskite structure leads to massive <i>M</i> and <i>X</i> vacancies in the 3D [<i>MX</i>₃] framework, thus the term hollow. The resulting materials are semiconductors with significantly blue-shifted direct band gaps from 1.25 to 1.51 eV for Sn-based perovskites and from 1.53 to 2.1 eV for the Pb-based analogues. The increased structural disorder and hollow nature were validated by single crystal X-ray diffraction analysis as well as pair distribution function (PDF) analysis. Density functional theory (DFT) calculations support the experimental trends and suggest that the observed widening of the band gap is attributed to the massive <i>M</i> and <i>X</i> vacancies, which create a less connected 3D hollow structure. The resulting materials have superior air stability, where in the case of Sn-based hollow perovskites it exceeds two orders of temporal magnitude compared to the conventional full perovskites of MASnI₃ and FASnI₃. The hollow perovskite compounds pose as a new platform of promising light absorbers that can be utilized in single junction or tandem solar cells