New Dication-Based Lead-Deficient 3D MAPbI3 and FAPbI3 "d-HPs" Perovskites with Enhanced Stability.

Toxicity induced by the presence of lead and the rather poor stability of halide perovskite semiconductors represent the major issues for their large-scale application. We previously reported a new family of lead- and iodide-deficient MAPbI3 and FAPbI3 perovskites called d-HPs (for lead- and iodide-deficient halide perovskites) based on two organic cations: hydroxyethylammonium HO-(CH2)2-NH3+ (HEA+) and thioethylammonium HS-(CH2)2-NH3+ (TEA+). In this article, we report the use of an organic dication, 2-hydroxypropane-1,3-diaminium (2-propanol 1,3 diammonium), named PDA2+, to create new 3D d-HPs based on the MAPbI3 and FAPbI3 network with general formulations of (PDA)0,88x(MA)1-0,76x[Pb1-xI3-x] and (PDA)1,11x(FA)1-1,22x[Pb1-xI3-x], respectively. These d-HPs have been successfully synthesized as crystals, powders, and thin films and exhibit improved air stability compared to their reference MAPbI3 and FAPbI3 perovskite counterparts. PDA2+-based deficient MAPbI3 was also tested in operational perovskite solar cells and exhibited an efficiency of 13.0% with enhanced stability.

Enhanced Stability and Band Gap Tuning of α-[HC(NH2)2]PbI3 Hybrid Perovskite by Large Cation Integration.

We report room-temperature synthesis of lead- and iodide-deficient α-[HC(NH2)2]PbI3 perovskites (abbreviated d-α-FAPI, FA+ = formamidinium), with the general formula (A',FA)1+ x[Pb1- xI3- x] (with A' = hydroxyethylammonium (HEA+) or thioethylammonium (TEA+) cations, 0.04 ≤ x ≤ 0.15). These materials retain a 3D character of their perovskite network despite incorporation of large HEA+ or TEA+ cations, demonstrating that the Goldschmidt tolerance factor can be bypassed. We found that thin films of (TEA,FA)1+ x[Pb1- xI3- x] ( x = 0.04 and 0.13) show exceptional α-phase stability under ambient conditions, 1 order of magnitude higher than α-FAPI and α-(Cs,FA)PbI3 thin films. d-α-FAPI phases are shown to maintain a direct band gap, which increases monotonously for x ranging from 0 up to 0.20, with characteristics of a p-type semiconductor for low concentrations of vacancies ( x ≤ 0.13) and n-type for larger ones. They offer alternatives to reach the methylammonium- and bromine-free stable α-FAPI-type phase and open new avenues in the field of perovskite solar cells, up to band gap tuning desirable for tandem solar cells.

Lead- and Iodide-Deficient (CH3 NH3 )PbI3 (d-MAPI): The Bridge between 2D and 3D Hybrid Perovskites.

3D and 2D hybrid perovskites, which have been known for more than 20 years, have emerged recently as promising materials for optoelectronic applications, particularly the 3D compound (CH3 NH3 )PbI3 (MAPI). The discovery of a new family of hybrid perovskites called d-MAPI is reported: the association of PbI2 with both methyl ammonium (MA+ ) and hydroxyethyl ammonium (HEA+ ) cations leads to a series of five compounds with general formulation (MA)1-2.48x (HEA)3.48x [Pb1-x I3-x ]. These materials, which are lead- and iodide-deficient compared to MAPI while retaining 3D architecture, can be considered as a bridge between the 2D and 3D materials. Moreover, they can be prepared as crystallized thin films by spin-coating. These new 3D materials appear very promising for optoelectronic applications, not only because of their reduced lead content, but also in account of the large flexibility of their chemical composition through potential substitutions of MA+ , HEA+ , Pb2+ and I- ions.

In low transpiring conditions, nitrate and water fluxes for growth of B. napus plantlets correlate with changes in BnNrt2.1 and BnNrt1.1 transporter expression.

We analyzed how changes in BnNrt nitrate transporter gene expression induced by nitrate are associated with morphological changes in plantlets and osmotic water flow for growth. We hypothesized that in a Petri dish system, reduction in transpiration should induce conditions where nitrate and water fluxes for growth depend directly on nitrate transporter activity and nitrate signaling. Rape seedlings growing on agar plates were supplied with increasing external K (15)NO 3 concentrations from 0.05 to 20 mM. After 5 d of treatment, morphological switches in plantlet growth were observed between 0.5 and 5 mM nitrate supply. Root elongation was reduced by 50% while the cotyledon surface area was doubled. These morphological switches were strongly associated with increases in (15)NO 3(-) and water uptake rates as well as (15)N and water allocation to the shoot. These switches were also highly correlated with the upregulation of BnNrt1.1 and BnNrt2.1 in the root. However, while root expression of BnNrt2.1 was correlated linearly with a shoot growth-associated increase in (15)N and water uptake, BnNrt1.1 expression was correlated exponentially with both (15)N and water accumulation. In low transpiring conditions, the tight control exercised by nitrate transporters on K (15)NO 3 uptake and allocation clearly demonstrates that they modulated the nitrate-signaling cascade involved in cell growth and as a consequence, water uptake and allocation to the growing organs. Deciphering this signaling cascade in relation to acid growth theory seems to be the most important challenge for our understanding of the nitrate-signaling role in plant growth.

In low transpiring conditions, uncoupling the BnNrt2.1 and BnNrt1.1 NO 3(-) transporters by glutamate treatment reveals the essential role of BnNRT2.1 for nitrate uptake and the nitrate-signaling cascade during growth.

In plants, the nitrate transporters, NRT1.1 and NRT2.1, are mainly responsible for nitrate uptake. Intriguingly, both nitrate transporters are located in a complementary manner in different cells layers of the mature root suggesting that their coordination should occur during nitrate uptake and plant growth. This hypothesis was examined on 5-d-old rape seedlings grown on agar medium supplemented with 1 or 5mM nitrate. Seedlings were treated with increasing potassium glutamate concentrations in order to uncouple the two nitrate transporters by inhibiting BnNRT2.1 expression and activity specifically. In both nitrate treatments, increasing the glutamate concentrations from 0.5 to 10mM induced a reduction in (15)NO 3(-) uptake and an inhibition of N assimilation. The decrease in (15)NO 3(-) uptake was caused by downregulation of BnNRT2.1 expression but surprisingly it was not compensated by the upregulation of BnNRT1.1. This created an unprecedented physiological situation where the effects of the nitrate signal on shoot growth were solely modulated by nitrate absorption. In these conditions, the osmotic water flow for volumetric shoot growth was mainly dependent on active nitrate transport and nitrate signaling. This behavior was confirmed by the allometric relationships found between changes in the root length with (15)N and water accumulation in the shoot. These findings demonstrate that the BnNRT2.1 transporter is essential for nitrate uptake and growth, and renew the question of the respective roles of the NRT2.1 and NRT1.1 transporters in nitrate uptake and sensing at the whole plant level.

Elongation changes of exploratory and root hair systems induced by aminocyclopropane carboxylic acid and aminoethoxyvinylglycine affect nitrate uptake and BnNrt2.1 and BnNrt1.1 transporter gene expression in oilseed rape.

Ethylene is a plant hormone that plays a major role in the elongation of both exploratory and root hair systems. Here, we demonstrate in Brassica napus seedlings that treatments with the ethylene precursor, aminocyclopropane carboxylic acid (ACC) and the ethylene biosynthesis inhibitor, aminoethoxyvinylglycine (AVG), cause modification of the dynamic processes of primary root and root hair elongation in a dose-dependent way. Moreover, restoration of root elongation in AVG-treated seedlings by 1 mm l-glutamate suggested that high concentrations of AVG affect root elongation through nonoverlapping ethylene metabolic pathway involving pyridoxal 5'-P-dependent enzymes of nitrate (N) metabolism. In this respect, treatments with high concentrations of ACC and AVG (10 mum) over 5 d revealed significant differences in relationships between root growth architecture and N uptake capacities. Indeed, if these treatments decreased severely the elongation of the exploratory root system (primary root and lateral roots) they had opposing effects on the root hair system. Although ACC increased the length and number of root hairs, the rate of N uptake and the transcript level of the N transporter BnNrt2.1 were markedly reduced. In contrast, the decrease in root hair length and number in AVG-treated seedlings was overcompensated by an increase of N uptake and BnNrt2.1 gene expression. These root architectural changes demonstrated that BnNrt2.1 expression levels were more correlated to the changes of the exploratory root system than the changes of the root hair system. The difference between treatments in N transporters BnNrt1.1 and BnNrt2.1 gene expression is discussed with regard to presumed transport functions of BnNrt1.1 in relation to root elongation.