No abstract

2D Ruddlesden−Popper (2DRP) tin (Sn) perovskite solar cells (PSCs) play an irreplaceable role in advancing the commercialization of perovskite-based photovoltaic devices due to their low toxicity and improved stability. However, the efficiency of 2DRP Sn PSCs has not made a breakthrough owing to incompletely oriented crystal growth and poor film morphology, which is limited by a complex and uncontrollable crystallization process. Here, we first introduce the mixed spacer organic cations [n-butylamine (BA) and phenylethylamine (PEA)] in 2DRP Sn perovskite to control the crystallization process. We find that when the BA + and PEA + cowork to form [(BA 0.5 PEA 0.5 ) 2 FA 3 Sn 4 I 13 ] 2DRP perovskites, the intermediate phase impeding the homogeneous and ordered nucleation of the crystal is suppressed effectively, thus enabling a high-quality film morphology and improved crystal orientation. Benefitting from it, the power conversion efficiency (PCE) is improved to 8.82%, which is the highest one among the 2DRP Sn PSCs as far as we known.

Dion–Jacobson (DJ) phase halide perovskites have attracted extensive attention in photovoltaic devices due to their significantly enhanced stability when compared with conventional 3D analogs. However, fundamental questions concerning the quantum well (QW) barrier thicknesses, which are critical to design efficient DJ phase perovskite photovoltaics, remain unknown. Herein, it is unambiguously demonstrated that QW barrier thickness, depending on bulky organic ammonium spacers with different chain lengths, such as 1.3‐propanediamine (PDA), 1.4‐butanediamine (BDA), 1.5‐pentamethylenediamine (PeDA), and 1.6‐hexamethylenediamine (HDA), allows the control of orientation and QW distribution. The DJ phase perovskites based on PDA and BDA have suitable QW barrier thicknesses, which exhibit excellent orientation and more uniform QW distribution, allowing a smooth bandgap transition that leads to longer carrier diffusion length, higher charge mobility, and lower defect density. Conversely, PeDA and HDA, with thicker QW barriers, result in lower orientation and multiple DJ perovskite phases. DJ phase perovskite photovoltaic devices based on PDA and BDA show significantly improved power conversion efficiencies (PCEs) of 14.16% and 16.38% compared with PCEs of 12.95% and 10.55% for PeDA and HDA analogs, respectively.

Tb 3 + – Yb 3 + codoped transparent oxyfluoride glass ceramics containing CaF2 nanocrystals were synthesized. The formation of CaF2 nanocrystals in the glass ceramics was confirmed by x-ray diffraction and high resolution transmission electron microscopy. The incorporation of Tb3+ and Yb3+ into CaF2 nanocrystal lattice was confirmed by energy dispersive spectroscopy. Infrared quantum cutting involving Yb3+ 950–1100nm (F5∕22→F7∕22) emission was achieved upon the excitation of D45 energy level of Tb3+ at 484nm. The photoluminescence properties have been studied for these glass ceramics. Yb3+ concentration dependent quantum efficiency was calculated, and the maximum efficiency approaches 155% before reaching concentration quenching threshold.

Due to the additional introduction of bulky organic ammonium and the competition between bulky organic ammonium and methyl ammonium in 2D Ruddlesden-Popper (2DRP) perovskite, the crystallization process becomes complicated. Here, it is demonstrated that the rapid crystallization controlled by processing solvents plays an important role in achieving highquality 2DRP perovskite films. It is found that the processing solvents, e.g., dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO), with a different polarity and boiling point, have almost no effect on crystal structure and phase distribution but have a remarkable effect on crystallization kinetics, crystal growth orientation, and crystallinity of 2DRP perovskite. Compared to polar aprotic solvent DMF and DMSO with a high boiling point, DMAC with low polarity and a suitable boiling point has a weak coordination to lead and ammonium salts and is easy to escape during solution processing, which is able to accelerate the crystallization rate of 2DRP perovskite. Benefitting from the rapid crystallization enabled high-quality 2DRP perovskite films, the best-performing device with improved stability and a power conversion efficiency of 12.15% is obtained using DMAC solvent. These findings may give guidance for solvent engineering for highly efficient 2DRP perovskite solar cells in the future.