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.
In the past years, hybrid perovskite materials have attracted great attention due to their superior optoelectronic properties. In this study, the authors report the utilization of cobalt (Co2+) to partially substitute lead (Pb2+) for developing novel hybrid perovskite materials, CH3NH3Pb1‐
- NSF-PAR ID:
- 10050410
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Energy Materials
- Volume:
- 8
- Issue:
- 14
- ISSN:
- 1614-6832
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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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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Abstract Hybrid halide 2D perovskites deserve special attention because they exhibit superior environmental stability compared with their 3D analogs. The closer interlayer distance discovered in 2D Dion–Jacobson (DJ) type of halide perovskites relative to 2D Ruddlesden–Popper (RP) perovskites implies better carrier charge transport and superior performance in solar cells. Here, the structure and properties of 2D DJ perovskites employing 3‐(aminomethyl)piperidinium (3AMP2+) as the spacing cation and a mixture of methylammonium (MA+) and formamidinium (FA+) cations in the perovskite cages are presented. Using single‐crystal X‐ray crystallography, it is found that the mixed‐cation (3AMP)(MA0.75FA0.25)3Pb4I13perovskite has a narrower bandgap, less distorted inorganic framework, and larger PbIPb angles than the single‐cation (3AMP)(MA)3Pb4I13. Furthermore, the (3AMP)(MA0.75FA0.25)3Pb4I13films made by a solvent‐engineering method with a small amount of hydriodic acid have a much better film morphology and crystalline quality and more preferred perpendicular orientation. As a result, the (3AMP)(MA0.75FA0.25)3Pb4I13‐based solar cells exhibit a champion power conversion efficiency of 12.04% with a high fill factor of 81.04% and a 50% average efficiency improvement compared to the pristine (3AMP)(MA)3Pb4I13cells. Most importantly, the 2D DJ 3AMP‐based perovskite films and devices show better air and light stability than the 2D RP butylammonium‐based perovskites and their 3D analogs.
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Abstract The energy level alignment that occurs at the interfaces in planar-hetero structured perovskite photovoltaic devices strongly influences the charge transport across the interface, and thus plays a crucial role in overall device performance. To directly observe the energy level alignment requires pristine homogeneous surfaces that are free of contamination including adventitious carbon. Co-evaporation offers the ability to grow perovskite thin films in-situ, and the method involves thermally evaporating the perovskite precursors such as PbI 2 and CH 3 NH 3 I. Early reports have shown that the perovskite film formation and stoichiometry are problematic at ultralow coverages. In particular, it was reported that there was excessive PbI 2 and a deficiency in CH 3 NH 3 I. Using photoemission spectroscopy, we investigated the perovskite precursor PbI 2 on gold and highly oriented pyrolytic graphite (HOPG) surfaces. Results show that the nature of the surface and the deposition conditions can strongly influence the film formation. Excessive iodine observed in the initial evaporation stages appears to be substrate dependent, and this may influence the overall energy level alignment.more » « less
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Abstract 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−
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.
