Understanding interfacial reactions that occur between the active layer and charge‐transport layers can extend the stability of perovskite solar cells. In this study, the exposure of methylammonium lead iodide (CH3NH3PbI3) thin films prepared on poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)‐coated glass to 70% relative humidity (R.H.) leads to a perovskite crystal structure change from tetragonal to cubic within 2 days. Interface‐sensitive photoluminescence measurements indicate that the structural change originates at the PEDOT:PSS/perovskite interface. During exposure to 30% R.H., the same structural change occurs over a much longer time scale (>200 days), and a reflection consistent with the presence of (CH3)2NH2PbI3is detected to coexist with the cubic phase by X‐ray diffraction pattern. The authors propose that chemical interactions at the PEDOT:PSS/perovskite interface, facilitated by humidity, promote the formation of dimethylammonium, (CH3)2NH2+. The partial A‐site substitution of CH3NH3+for (CH3)2NH2+to produce a cubic (CH3NH3)1−
The surface of CH3NH3PbBr3perovskite nanocrystals (PNCs) plays a critical role in determining their optical properties and stability. The introduction of capping ligands can enhance photoluminescence (PL), reduce non‐radiative recombination, and improve stability. Here, we report a facile synthesis of CH3NH3PbBr3PNCs with strong and highly stable green PL using melamine (Mela) as a simple and low‐cost capping ligand. The resulting CH3NH3PbBr3/Mela PNCs have cubic phase crystal structure with an average particle size of 5.29±0.06 nm. The optical absorption and PL of the CH3NH3PbBr3/Mela PNCs with narrow bandwidth can be tuned within the visible region, and the PL quantum yield (QY) reached 52.3% compared to 0.4% the pristine CH3NH3PbBr3PNCs. A synergistic effect between NH3+and the electron‐rich nitrogen atoms together with p‐p stacking capacity, likely contributes to enhance the PL by effectively passivating of the trap states of PNCs. Furthermore, melamine‐capped PNCs show high stability in protic solvents as a result of the steric bulkiness of the triazine rings, owing to the planar structure together with hydrogen bonding of melamine, which prevents solvent molecules from reaching and reacting with the core of PNCs. This study demonstrates a simple and effective approach for stabilizing PNCs for potential applications such as solar cells and LEDs.
more » « less- PAR ID:
- 10054052
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemNanoMat
- Volume:
- 4
- Issue:
- 4
- ISSN:
- 2199-692X
- Page Range / eLocation ID:
- p. 409-416
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract x [(CH3)2NH2]x PbI3phase explains the structural change from tetragonal to cubic during short‐term humidity exposure. When (CH3)2NH2+content exceeds its solubility limit in the perovskite during longer humidity exposures, a (CH3)2NH2+‐rich, hexagonal phase of (CH3NH3)1−x [(CH3)2NH2]x PbI3emerges. These interfacial interactions may have consequences for device stability and performance beyond CH3NH3PbI3model systems and merit close attention from the perovskite research community. -
Recent progress has been made on the synthesis and characterization of metal halide perovskite magic-sized clusters (PMSCs) with ABX 3 composition ( A = C H 3 N H 3 + or Cs + , B = P b 2 + , and X = C l − , Br - , or I - ). However, their mechanism of growth and structure is still not well understood. In our effort to understand their structure and growth, we discovered that a new species can be formed without the CH 3 NH 3 + component, which we name as molecular clusters (MCs). Specifically, CH 3 NH 3 PbBr 3 PMSCs, with a characteristic absorption peak at 424 nm, are synthesized using PbBr 2 and CH 3 NH 3 Br as precursors and butylamine (BTYA) and valeric acid (VA) as ligands, while MCs, with an absorption peak at 402 nm, are synthesized using solely PbBr 2 and BTYA, without CH 3 NH 3 Br. Interestingly, PMSCs are converted spontaneously overtime into MCs. An isosbestic point in their electronic absorption spectra indicates a direct interplay between the PMSCs and MCs. Therefore, we suggest that the MCs are precursors to the PMSCs. From spectroscopic and extended X-ray absorption fine structure (EXAFS) results, we propose some tentative structural models for the MCs. The discovery of the MCs is critical to understanding the growth of PMSCs as well as larger perovskite quantum dots (PQDs) or nanocrystals (PNCs).more » « less
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Abstract Organic–inorganic halide perovskites are promising photodetector materials due to their strong absorption, large carrier mobility, and easily tunable bandgap. Up to now, perovskite photodetectors are mainly based on polycrystalline thin films, which have some undesired properties such as large defective grain boundaries hindering the further improvement of the detector performance. Here, perovskite thin‐single‐crystal (TSC) photodetectors are fabricated with a vertical p–i–n structure. Due to the absence of grain‐boundaries, the trap densities of TSCs are 10–100 folds lower than that of polycrystalline thin films. The photodetectors based on CH3NH3PbBr3and CH3NH3PbI3TSCs show low noise of 1–2 fA Hz−1/2, yielding a high specific detectivity of 1.5 × 1013cm Hz1/2W−1. The absence of grain boundaries reduces charge recombination and enables a linear response under strong light, superior to polycrystalline photodetectors. The CH3NH3PbBr3photodetectors show a linear response to green light from 0.35 pW cm−2to 2.1 W cm−2, corresponding to a linear dynamic range of 256 dB.
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Abstract The chemical stabilities of hybrid perovskite materials demand further improvement toward long‐term and large‐scale photovoltaic applications. Herein, the enhanced chemical stability of CH3NH3PbI3is reported by doping the divalent anion Se2−in the form of PbSe in precursor solutions to enhance the hydrogen‐bonding‐like interactions between the organic cations and the inorganic framework. As a result, in 100% humidity at 40 °C, the 10% w/w PbSe‐doped CH3NH3PbI3films exhibited >140‐fold stability improvement over pristine CH3NH3PbI3films. As the PbSe‐doped CH3NH3PbI3films maintained the perovskite structure, a top efficiency of 10.4% with 70% retention after 700 h aging in ambient air is achieved with an unencapsulated 10% w/w PbSe:MAPbI3‐based cell. As a bonus, the incorporated Se2−also effectively suppresses iodine diffusion, leading to enhanced chemical stability of the silver electrodes.
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