2D perovskites have emerged as one of the most promising photovoltaic materials owing to their excellent stability compared with their 3D counterparts. However, in typical 2D perovskites, the highly ...conductive inorganic layers are isolated by large organic cations leading to quantum confinement and thus inferior electrical conductivity across layers. To address this issue, the large organic cations are replaced with small propane‐1,3‐diammonium (PDA) cations to reduce distance between the inorganic perovskite layers. As shown by optical characterizations, quantum confinement is no longer dominating in the PDA‐based 2D perovskites. This leads to considerable enhancement of charge transport as confirmed with electrochemical impedance spectroscopy, time‐resolved photoluminescence, and mobility measurements. The improved electric properties of the interlayer‐engineered 2D perovskites yield a power conversion efficiency of 13.0%. Furthermore, environmental stabilities of the PDA‐based 2D perovskites are improved. PDA‐based 2D perovskite solar cells (PSCs) with encapsulation can retain over 90% of their efficiency upon storage for over 1000 h, and PSCs without encapsulation can maintain their initial efficiency at 70 °C for over 100 h, which exhibit promising stabilities. These results reveal excellent optoelectronic properties and intrinsic stabilities of the layered perovskites with reduced interlayer distance.
2D perovskites with reduced interlayer distance are synthesized by using propane‐1,3‐diammonium (PDA). The quantum‐confinement effect that is usually observed in 2D perovskites is minimized in the engineered 2D perovskites, which facilitates charge transport between inorganic layers. With enhanced charge‐transport properties, PDA2MA3Pb4I13 perovskite solar cells yield an efficiency up to 13.0% and exhibit better stability.
Formation of a single‐component charge‐transfer complex (SCCTC) is unveiled in solid state of an intermolecular charge‐transfer molecule ...2‐(4‐(1‐phenyl‐1H‐phenanthro9,10‐dimidazol‐2‐yl)phenyl)anthracene‐9,10‐dione (PIPAQ). Intermolecular donor–acceptor interactions between two PIPAQ molecules is the primary driving force for self‐association and contributes to intermolecular charge transfer. The SCCTC character is fully verified by crystallographic, photophysical, electron spin resonance, and vibrational characterizations. The PIPAQ‐based SCCTC is first applied in light‐emitting devices as an emissive layer to realize efficient deep‐red/near‐infrared electroluminescence. This work provides new insights into SCCTC and represents an important step toward their applications in optoelectronic devices.
Dimeric single‐component charge‐transfer complexes (SCCTCs) by self‐complexation of a donor–π–acceptor molecule (PIPAQ) are revealed and fully investigated, wherein the strong intermolecular charge transfer leads to unprecedented deep‐red/near‐infrared emission. The SCCTCs can be formed in thin films and applied in electroluminescence devices to realize high efficiencies via a thermally activated delayed fluorescence channel.
It has been generally believed and assumed that organometal halide perovskites would form type II P–N junctions with fullerene derivatives (C60 or PCBM), and the P–N junctions would provide driving ...force for exciton dissociation in perovskite‐based solar cell. To the best of our knowledge, there is so far no experiment proof on this assumption. On the other hand, whether photogenerated excitons can intrinsically dissociate into free carrier in the perovskite without any assistance from a P–N junction is still controversial. To address these, the interfacial electronic structures of a vacuum‐deposited perovskite/C60 and a solution‐processed perovskite/PCBM junctions is directly measured by ultraviolet photoelectron spectroscopy. Contrary to the common believes, both junctions are found to be type I N–N junctions with band gap of the perovskites embedded by that of the fullerenes. Meanwhile, device with such a charge inert junction can still effectively functions as a solar cell. These results give direct experimental evidence that excitons are dissociated to free carriers in the perovskite film even without any assistance from a P–N junction.
While perovskites/fullerene is commonly assumed to form a type II P–N junction with its internal E‐field facilitating exciton dissociation, it is found that perovskite/C60 (PCBM) is a charge inert type I N–N junction. Devices with such a junction show photovoltaic effects effectively, thus photogenerated excitons can indeed dissociate to free carriers in the perovskite film.
Methylammonium (CH3NH3+) and formamidinium ((NH2)2CH+) based lead iodide perovskites are currently the two commonly used organic–inorganic lead iodide perovskites. There are still no alternative ...organic cations that can produce perovskites with band gaps spanning the visible spectrum (that is, <1.7 eV) for solar cell applications. Now, a new perovskite using large propane‐1,3‐diammonium cation (1,3‐Pr(NH3)22+) with a chemical structure of (1,3‐Pr(NH3)2)0.5PbI3 is demonstrated. X‐ray diffraction (XRD) shows that the new perovskite exhibits a three‐dimensional tetragonal phase. The band gap of the new perovskite is about 1.6 eV, which is desirable for photovoltaic applications. A (1,3‐Pr(NH3)2)0.5PbI3 perovskite solar cell (PSC) yields a power conversion efficiency (PCE) of 5.1 %. More importantly, this perovskite is composed of a large hydrophobic cation that provides better moisture resistance compared to CH3NH3PbI3 perovskite.
Large and in charge: A perovskite (1,3‐Pr(NH3)2)0.5PbI3) was prepared using the large propane‐1,3‐diammonium cation (1,3‐Pr(NH3)22+). This perovskite shows 3D structure and a band gap of about 1.6 eV spanning the visible spectrum for solar cell applications. It is composed of a larger organic cation that provides better moisture resistance compared to CH3NH3PbI3 perovskite.
Two-dimensional (2D) perovskites with n = 4 have attracted much attention recently and the low-n ( e.g. n = 1) phases in these 2D perovskites have been found to act as carrier traps, leading to ...decreased performance. In this work, we demonstrate a simple method to suppress the formation of low-n phases by using dimethyl sulfoxide (DMSO) as a co-solvent. The present 2D perovskites with alternating cations in the interlayer space (ACI) exhibit enhanced carrier lifetime and charge transport by suppressing low-n phases. The optimized 2D ACI-based perovskite solar cell shows a PCE of 12.8%, which is also the highest efficiency for ACI-based perovskite solar cells, and is almost 3 times higher than that of the non-DMSO treated devices.
The exact hosts for F‐P hybrid WOLEDs have been first demonstrated following a new design strategy for blue fluorophors with small singlet‐triplet splitting. Two novel compounds DPMC and DAPSF ...exhibit efficient blue fluorescence, high triplet energies and good conductivities. These merits allow us to use new simplified device designs to achieve high efficiency, slow efficiency roll‐off and stable emission color.
Stabilization of two-dimensional (2D) PEA2PbI4 (PEA is phenethylammonium) perovskite nanocrystals (PNCs) in water is achieved. By inhibiting the desorption process, the PNCs show exceptional ...stability for more than 2 months in PEA+ aqueous solutions. Stabilized PNCs are successfully applied for probing Cu2+ in aqueous solution.
We show the effects of chlorine incorporation in the crystallization process of perovskite film based on a lead acetate precursor. We demonstrate a fabrication process for fast grain growth with ...highly preferred {110} orientation upon only 5 min of annealing at 100 °C. By studying the correlation between precursor composition and morphology, the growth dynamic of perovskite film in the current system is discussed. In particular, we found that both lead acetate precursor and Cl incorporation are beneficial to perovskite growth. While lead acetate allows fast crystallization process, Cl improves perovskite crystallinity. Planar perovskite solar cells with optimized parameters deliver a best power conversion efficiency of 15.0% and average efficiency of 14.0% with remarkable reproducibility and good stability.
Molecular level one-dimensional (1D) metal halide perovskites possessing large exciton binding energies are generally considered unfavorable for photovoltaic devices. To date, applying 1D perovskites ...as active materials for solar cells has not been as well explored as 3D and 2D perovskites. Herein, we report a new low-dimensional hybrid perovskite based on 1D 1,4-benzene diammonium lead iodide (BDAPbI 4 ) perovskite. Counterintuitive to the general belief, a high efficiency of up to 14% was achieved for solar cells based on low-dimensional hybrid perovskites containing 1D BDAPbI 4 and 3D MAPbI 3 . More importantly, these solar cells can retain over 95% of their efficiency upon storage for over 1000 h and show impressive stability under continuous illumination and heating.
Although Cl-doping is a common technique for achieving high photovoltaic (PV) performance, the Cl content is negligibly small and cannot easily be tuned. Therefore, we herein study the formation ...chemistry of Cl-doped perovskites by examining the chemical interactions between thermally evaporated MAI and PbCl sub(2) through X-ray photoemission spectroscopy (XPS). We show that PbCl sub(2) is not stable at the MAI/PbCl sub(2) contact surface. The Cl atom readily detaches from the PbCl sub(2), which subsequently initiates electron transition from Pb to MAI. Viathermal-evaporation, a perovskite with a high PbCl sub(2) content can be prepared and examined. We found that the presence of metallic Pb, associated with increased Cl content, can quench the photogenerated exciton in PV devices. By optimizing the ratio of MAI : PbCl sub(2), a perovskite solar cell with similar to 6% efficiency was obtained.
