We demonstrate strong potential of computational screening and germanium iodide perovskite compounds for photovoltaic applications.

A lead-free low bandgap organic-inorganic hybrid perovskite, formamidinium tin iodide, is utilized as a light absorbing layer in photovoltaics. This material has a bandgap of 1.41 eV which allows light harvesting from the near infrared region, making high photocurrents achievable. A power conversion efficiency of 2.10% was accomplished upon incorporating SnF 2 .

Replacement of lead in the hybrid organic–inorganic perovskite solar cells invokes the need for non-toxic materials such as Sn. Although solution processed CsSnI3 has been demonstrated as a lead-free halide perovskite which can function as a light absorber with high photocurrent densities, the power conversion efficiencies were bottlenecked by low open circuit voltages. In this work, the open circuit voltages are modulated by chemical doping of CsSnI3 with Br leading to formation of CsSnI3‑x Br x (0 ≤ x ≤ 3) perovskites. The beneficial effect of Br incorporation for V oc improvement is evident for CsSnI3 system even without the addition of SnF2. There is an evolution of the crystal structure of CsSnI3 from orthorhombic to cubic for CsSnBr3 accompanied by changes in its optical properties with a blue shift of the absorption and IPCE onset, as the Br– doping is increased. The V oc enhancement is attributed to the decrease in Sn vacancies which is reflected by the lower charge carrier densities of 1015 cm–3 and a high resistance to charge recombination in case of Br rich CsSnI3‑x Br x perovskite. By the addition of SnF2 to CsSnI3‑x Br x perovskite, the current densities are improved significantly.

Even though perovskite solar cells have reached 22% efficiency within a very short span, the presence of lead is a major bottleneck to its commercial application. Tin and Germanium based perovskites failed to be viable replacements due to the instability of their +2 oxidation states. Antimony could be a possible replacement, forming perovskites with structure A3M2X9. However, solution processing of Cs, organic ammonium based Sb perovskites result in the formation of the dimer phase with poor charge transport properties. Here we demonstrate that Rb can template the formation of the desired layered phase irrespective of processing methodologies, enabling the demonstration of efficient lead-free perovskite solar cells.

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.

A new spin on perovskites untwined: Ultrafast optical switching and tuning of spin-energy states in layered halide perovskites.

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.

A novel swivel-cruciform 3,3′-bithiophene based hole-transporting material (HTM) with a low lying highest occupied molecular orbital (HOMO) level for application in perovskite solar cells were synthesized.