High-performance and good-stability hollow Sn-based perovskite solar cells using ethylenediammonium and formamidinium cations.

The molecular building block approach was employed effectively to construct a series of novel isoreticular, highly porous and stable, aluminum-based metal–organic frameworks with soc topology. From this platform, three compounds were experimentally isolated and fully characterized: namely, the parent Al-soc-MOF-1 and its naphthalene and anthracene analogues. Al-soc-MOF-1 exhibits outstanding gravimetric methane uptake (total and working capacity). It is shown experimentally, for the first time, that the Al-soc-MOF platform can address the challenging Department of Energy dual target of 0.5 g/g (gravimetric) and 264 cm3 (STP)/cm3 (volumetric) methane storage. Furthermore, Al-soc-MOF exhibited the highest total gravimetric and volumetric uptake for carbon dioxide and the utmost total and deliverable uptake for oxygen at relatively high pressures among all microporous MOFs. In order to correlate the MOF pore structure and functionality to the gas storage properties, to better understand the structure–property relationship, we performed a molecular simulation study and evaluated the methane storage performance of the Al-soc-MOF platform using diverse organic linkers. It was found that shortening the parent Al-soc-MOF-1 linker resulted in a noticeable enhancement in the working volumetric capacity at specific temperatures and pressures with amply conserved gravimetric uptake/working capacity. In contrast, further expansion of the organic linker (branches and/or core) led to isostructural Al-soc-MOFs with enhanced gravimetric uptake but noticeably lower volumetric capacity. The collective experimental and simulation studies indicated that the parent Al-soc-MOF-1 exhibits the best compromise between the volumetric and gravimetric total and working uptakes under a wide range of pressure and temperature conditions.

The unique hybrid nature of 2D Ruddlesden–Popper (R–P) perovskites has bestowed upon them not only tunability of their electronic properties but also high-performance electronic devices with improved environmental stability as compared to their 3D analogs. However, there is limited information about their inherent heat, light, and air stability and how different parameters such as the inorganic layer number and length of organic spacer molecule affect stability. To gain deeper understanding on the matter we have expanded the family of 2D R–P perovskites, by utilizing pentylamine (PA)2(MA) n−1Pb n I3n+1 (n = 1–5, PA = CH3(CH2)4NH3 +, C5) and hexylamine (HA)2(MA) n−1Pb n I3n+1 (n = 1–4, HA = CH3(CH2)5NH3 +, C6) as the organic spacer molecules between the inorganic slabs, creating two new series of layered materials, for up to n = 5 and 4 layers, respectively. The resulting compounds were extensively characterized through a combination of physical and spectroscopic methods, including single crystal X-ray analysis. High resolution powder X-ray diffraction studies using synchrotron radiation shed light for the first time to the phase transitions of the higher layer 2D R–P perovskites. The increase in the length of the organic spacer molecules did not affect their optical properties; however, it has a pronounced effect on the air, heat, and light stability of the fabricated thin films. An extensive study of heat, light, and air stability with and without encapsulation revealed that specific compounds can be air stable (relative humidity (RH) = 20–80% ± 5%) for more than 450 days, while heat and light stability in air can be exponentially increased by encapsulating the corresponding films. Evaluation of the out-of-plane mechanical properties of the corresponding materials showed that their soft and flexible nature can be compared to current commercially available polymer substrates (e.g., PMMA), rendering them suitable for fabricating flexible and wearable electronic devices.

Tin-based perovskites have very comparable electronic properties to lead-based perovskites and are regarded as possible lower toxicity alternates for solar cell applications. However, the efficiency of tin-based perovskite solar cells is still low and they exhibit poor air stability. Here, we report lead-free tin-based solar cells with greatly enhanced performance and stability using so-called "hollow" ethylenediammonium and methylammonium tin iodide ({en}MASnI) perovskite as absorbers. Our results show that en can improve the film morphology and most importantly can serve as a new cation to be incorporated into the 3D MASnI lattice. When the cation of en becomes part of the 3D structure, a high density of SnI vacancies is created resulting in larger band gap, larger unit cell volume, lower trap-state density, and much longer carrier lifetime compared to classical MASnI. The best-performing {en}MASnI solar cell has achieved a high efficiency of 6.63% with an open circuit voltage of 428.67 mV, a short-circuit current density of 24.28 mA cm, and a fill factor of 63.72%. Moreover, the {en}MASnI device shows much better air stability than the neat MASnI device. Comparable performance is also achieved for cesium tin iodide solar cells with en loading, demonstrating the broad scope of this approach.

All-inorganic perovskites have a special place in halide perovskite family because of their potential for better stability. However, the representative cesium lead iodide (CsPbI3) is metastable and spontaneously converts to the non-perovskite structure at room temperature. Here, we demonstrate that what appears to be all-inorganic CsPbI3 stabilized in its perovskite form using the purported intermediate known as hydrogen lead iodide (HPbI3) is, in fact, the hybrid perovskite cesium dimethylammonium lead iodide (Cs1−xDMAxPbI3, x = 0.2 to 0.5). Thus, many of the reported all-inorganic perovskites are actually still hybrid organic-inorganic perovskites, as strongly evidenced by a wide battery of experimental techniques presented here. Solar cells based on the representative composition Cs0.7DMA0.3PbI3 can achieve an average power conversion efficiency of 9.27 ± 1.28% (max 12.62%). These results provide an alternative angle to look at previous results pertaining all-inorganic CsPbI3 while the DMA cation is now revealed as an alternative A site cation.

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X-ray detectors have attracted significant attention because they are widely used in applications such as computed tomography (CT), homeland security, and environmental monitoring. [1,2] In particular, there is an ever-increasing demand to invent better semiconductor material and device design to attain even higher sensitivity and lower manufacturing cost. [3,4] In the past decades, various traditional semiconductors have been studied for X-ray detection applications, like silicon (Si), [5] high-purity germanium (HP-Ge), [6] amorphous selenium (α-Se), [7] mercury iodide (HgI 2), [8] cadmium zinc telluride (CdZnTe), [9] and so on. Unfortunately, none of them is very ideal, more specifically, neither HP-Ge nor CdZnTe is costeffective; Si and CdZnTe require high working voltage; Si and α-Se have low X-ray absorption coefficient and large leakage current. Also, the CdZnTe, Si, and HP-Ge require very high growth temperature exceeding 500 °C, Hg and Cd are highly toxic. Recently, solution-processable organic-inorganic metal-halide perovskites have been demonstrated as a promising candidate for high performance X-ray detectors. They are advantageous in strong X-ray absorption, processable at low temperature, low-cost fabrication, and superior semiconducting properties like low defect density, large mobility-lifetime product (μτ), long carrier diffusion length, etc. Noticeably, the recently reported X-ray detectors based on 3D perovskites including MAPbI 3 [4,10-12] and CsFAMA [13] microcrystalline thin films or MAPbX 3 (X = Cl, Br, I and their mixture), [14-24] Cs x FA 1−x PbI 3 , [25] CsPbBr 3 , [26-29] and Cs 2 AgBiBr 6 [30-32] single crystals have realized high sensitivity with the highest up to 2.1 × 10 4 µC Gy air-1 cm-2 , significantly larger than the state-of-the-art α-Se X-ray detectors. [33] Unfortunately, the dark current is too high and as is the photocurrent drift in X-ray detectors made of these hybrid organic and inorganic 3D perovskites, and this is expected based on serious ion migration in the materials. Even worse, ionic migration is recognized as the main root cause for material decomposition and performance degradation in perovskite devices. In order to obtain perovskites with low ion migration, low-dimensional perovskite single crystals, like inchsized 0D MA 3 Bi 2 I 9 [34-37] and Cs 3 Bi 2 I 9 , [38-40] 2D Cs 2 TeI 6 [41] and (NH 4) 3 Bi 2 I 9 , [42] have been adventured first by our group and Low ionic migration is required for a semiconductor material to realize stable high-performance X-ray detection. In this work, successful controlled incorporation of not only methylammonium (MA +) and cesium (Cs +) cations, but also bromine (Br-) anions into the FAPbI 3 lattice to grow inch-sized stable perovskite single crystal (FAMACs SC) is reported. The smaller cations and anions, comparing to the original FA + and Ihelp release lattice stress so that the FAMACs SC shows lower ion migration, enhanced hardness, lower trap density, longer carrier lifetime and diffusion length, higher charge mobility and the...

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) AMX perovskites ( A = methylammonium (MA), formamidinium (FA); M = Sn, Pb; X = Cl, Br, I), where small molecules such as ethylenediammonium cations ( en) 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, H NMR, TGA, SEM/EDX), we have assigned the general formula (A)( en) (M)(X) to the hollow perovskites. The incorporation of en in the 3D perovskite structure leads to massive M and X vacancies in the 3D [ MX] 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 M and X 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 MASnI and FASnI. The hollow perovskite compounds pose as a new platform of promising light absorbers that can be utilized in single junction or tandem solar cells.