Hybrid two-dimensional (2D) lead halide perovskites have been employed in optoelectronic applications, including white light emission for light emitting diodes (LEDs). However, until now, there have been limited reports on white light emitting lead halide perovskites with experimental insights into the mechanism of the broad band emission. Here, we present white light emission from a 2D hybrid lead chloride perovskite, using the widely known phenethylammonium cation. The single crystal X-ray structural data, time-resolved photophysical measurements, and DFT calculations are consistent with broad band emission arising from strong exciton-phonon coupling with the organic lattice, which is independent of surface defects. The phenethylammonium lead chloride material exhibits a remarkably high color rendering index of 84, CIE coordinate of (0.37,0.42), CCT of 4426, and photostability, making it ideal for natural white LEDs applications.

The electronic structure and energetic stability of A 2 BX 6 halide compounds with the cubic and tetragonal variants of the perovskite-derived K 2 PtCl 6 prototype structure are investigated computationally within the frameworks of density-functional-theory (DFT) and hybrid (HSE06) functionals. The HSE06 calculations are undertaken for 1 arXiv:1706.08674v1 [cond-mat.mtrl-sci] 27 Jun 2017 seven known A 2 BX 6 compounds with A = K, Rb and Cs, and B = Sn, Pd, Pt, Te, and X = I. Trends in band gaps and energetic stability are identified, which are explored further employing DFT calculations over a larger range of chemistries, characterized by A = K, Rb, Cs, B = Si, Ge, Sn, Pb, Ni, Pd, Pt, Se and Te and X = Cl, Br, I. For the systems investigated in this work, the band gap increases from iodide to bromide to chloride. Further, variations in the A site cation influences the band gap as well as the preferred degree of tetragonal distortion. Smaller A site cations such as K andRb favor tetragonal structural distortions, resulting in a slightly larger band gap. For variations in the B site in the (Ni, Pd, Pt) group and the (Se, Te) group, the band gap increases with increasing cation size. However, no observed chemical trend with respect to cation size for band gap was found for the (Si, Sn, Ge, Pb) group. The findings in this work provide guidelines for the design of halide A 2 BX 6 compounds for potential photovoltaic applications.

Perovskite solar cells, with efficiencies of 22.1%, are the only solution-processable technology to outperform multicrystalline silicon and thin-film solar cells. Whereas substantial progress has been made in scalability and stability, toxicity concerns drive the need for lead replacement, intensifying research into the broad palette of elemental substitutions, solid solutions, and multidimensional structures. Perovskites have gone from comprising three to more than eight (CH 3 NH 3 , HC(NH 2 ) 2 , Cs, Rb, Pb, Sn, I, Br) organic and inorganic constituents, and a variety of new embodiments including layered, double perovskites, and metal-deficient perovskites are being explored. Although most experimentation is guided by intuition and trial-and-error-based Edisonian approaches, rational strategies underpinned by computational screening and targeted experimental validation are emerging. In addressing emergent perovskites, this perspective discusses the rational design methodology leveraging densityfunctional-theory-based high-throughput computational screening coupled to downselection strategies to accelerate the discovery of materials and industrialization of perovskite solar cells.T he organic−inorganic hybrid perovskites 1−3 have emerged in recent years as an exceptional class of materials delivering >22% solar cell conversion efficiencies, displaying promising light-emission properties, and exhibiting extraordinary phenomena relating to spintronics, photostriction, laser-cooling, and long-wavelength radiation detection, among others. 4−6 These phenomena have been made possible by intrinsic properties of halide perovskites, exemplified by MAPbI 3 (MA = CH 3 NH 3 ), that include defect-free, crystalline film formation at <100 °C, high optical absorption/emission with wavelength tunability, long-range ambipolar transport, efficient charge transfer, and injection to and from metallic contacts. These superior properties have been made possible by synergistic effects of the perovskite symmetry (monovalent cation, e.g., MA + , contained within a cuboctahedral cage comprising MX 6 metal halides) and lone-pair s orbitals that yield direct band gap p−p transitions. 7 Despite the promising progress in high-efficiency solar cells, 8−14 long-term stability and toxicity concerns due to the 47 presence of lead are two key issues that must be addressed 48 before any market viability of perovskite solar cells could be 49 suggested. Fortuitously, perovskites offer a multitude of crys-50 tallographic configurations, along with a wide palette of sub-51 stituents that portend the promise of new and exciting 52 optoelectronic characteristics and enhanced device performance 53 p while resolving concerns of stability and toxicity. 54 Whereas stability issues are mainly being addressed through 55 multication substitution, carbon encapsulation, and incorpo-56 ration of hydrophobic moieties, the toxicity concern has taken a 57 distinct route that relies on replacing Pb with divalent, trivalent, 58 or tetravalent cations in perovskite and...

No abstract

No abstract