• Energy Research

In this report, we study a range of 2-D perovskite-like compounds (CH3NH3)2MPs2X2(M = Sn, Pb; Ps = OCN, SCN, SeCN and X = Cl, Br I), finding suitable band gaps, band alignments and defect behaviour for photovoltaic top cells in tandem devices.

In this report, we study a range of 2-D perovskite-like compounds (CH3NH3)2MPs2X2(M = Sn, Pb; Ps = OCN, SCN, SeCN and X = Cl, Br I), finding suitable band gaps, band alignments and defect behaviour for photovoltaic top cells in tandem devices.

Hybrid organic–inorganic halide perovskites are promising materials for thin-film solar cells. However, the toxicity and instability of best-in-class lead–halide perovskite materials make them nonideal. To combat these issues, we replaced lead with bismuth and explored the sensitivity of these new lead-free materials to the valency and bonding of their cationic organic groups. Specifically, we synthesized and characterized the materials properties and photophysical properties of hexane-1,6-diammonium bismuth pentaiodide ((HDA2+)BiI5) and compared them to an analogue containing a more volatile organic group with half the number of carbon and nitrogen atoms in the form of n-propylammonium ((PA+)xBiI3+x, where 1 < x < 3). The full crystallographic structures of (HDA2+)BiI5 and (PA+)xBiI3+x were resolved by single-crystal X-ray diffraction. (HDA2+)BiI5 was shown to be pure-phase and have a one-dimensional structure, whereas (PA+)xBiI3+x was shown to be a mix of one-dimensional and zero-dimensional phases. Str...

Hybrid organic–inorganic halide perovskites are promising materials for thin-film solar cells. However, the toxicity and instability of best-in-class lead–halide perovskite materials make them nonideal. To combat these issues, we replaced lead with bismuth and explored the sensitivity of these new lead-free materials to the valency and bonding of their cationic organic groups. Specifically, we synthesized and characterized the materials properties and photophysical properties of hexane-1,6-diammonium bismuth pentaiodide ((HDA2+)BiI5) and compared them to an analogue containing a more volatile organic group with half the number of carbon and nitrogen atoms in the form of n-propylammonium ((PA+)xBiI3+x, where 1 < x < 3). The full crystallographic structures of (HDA2+)BiI5 and (PA+)xBiI3+x were resolved by single-crystal X-ray diffraction. (HDA2+)BiI5 was shown to be pure-phase and have a one-dimensional structure, whereas (PA+)xBiI3+x was shown to be a mix of one-dimensional and zero-dimensional phases. Str...

Prediction of crystal stability and synthesisability is crucial for accelerated materials design. We discuss modern free energy methods for building more accurate models and data-driven approaches suitable for screening large chemical spaces.

Prediction of crystal stability and synthesisability is crucial for accelerated materials design. We discuss modern free energy methods for building more accurate models and data-driven approaches suitable for screening large chemical spaces.

As photovoltaics become an ever more important part of the global energy economy, the search for inexpensive, earth-abundant solar absorbers has grown rapidly. The binary compounds PbS and Bi2S3 have both seen success in previous photovoltaic studies; however, bulk PbS has a small band gap, restricting its efficiency, and Bi2S3, while strongly absorbing, can be limited by its layered structure. The mixed PbS–Bi2S3 series has previously been the focus of mostly structural studies, so in this article, we examine the electronic structure of the known members of this series using hybrid density functional theory. We find that the lead bismuth sulfides are able to retain optimal properties, such as low carrier effective masses and strong absorption, from both parent phases, with band gaps between 0.25 and 1.32 eV. PbBi2S4 emerges from our computational screening as a possible earth-abundant solar absorber, with a predicted maximum efficiency of 26% at a film thickness of 0.2 μm and with the retention of the th...