Chemical doping can be used to control the charge-carrier polarity and concentration in two-dimensional van der Waals materials. However, conventional methods based on substitutional doping or surface functionalization result in the degradation of
electrical mobility due to structural disorder, and the maximum doping density is set by the solubility limit of dopants. Here we show that a reversible laser-assisted chlorination process can be used to create high doping concentrations (above 3 × 1013 cm−2)
in graphene monolayers with minimal drops in mobility. The approach uses two lasers—with distinct photon energies and geometric configurations—that are designed for chlorination and subsequent chlorine removal, allowing highly doped patterns to
be written and erased without damaging the graphene. To illustrate the capabilities of our approach, we use it to create rewritable photoactive junctions for graphene-based photodetectors.
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Modulation Doping via a Two-Dimensional Atomic Crystalline Acceptor
Two-dimensional nanoelectronics, plasmonics, and emergent phases require clean and local charge control, calling for layered, crystalline acceptors or donors. Our Raman, photovoltage, and electrical conductance measurements combined with ab initio
calculations establish the large work function and narrow bands of α-RuCl3 enable modulation doping of exfoliated single and bilayer graphene, chemical vapor deposition grown graphene and WSe2, and molecular beam epitaxy grown EuS. We further demonstrate proof of principle photovoltage devices, control via twist angle, and charge transfer through hexagonal boron nitride. Short-ranged lateral doping (≤65 nm) and high homogeneity are achieved in proximate materials with a single layer of α-RuCl3. This leads to the best-reported monolayer graphene mobilities (4900 cm2 /(V s)) at
these high hole densities (3 × 1013 cm−2 ) and yields larger charge transfer to bilayer graphene (6 × 1013 cm−2).
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- Award ID(s):
- 1700137
- NSF-PAR ID:
- 10251486
- Date Published:
- Journal Name:
- Nano letters
- Volume:
- 20
- ISSN:
- 1530-6992
- Page Range / eLocation ID:
- 8446-8452
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Improving efficiency and stability has become an urgent issue in the application of perovskite solar cells (PSCs). Herein, a kind of long‐chain polymer or polymethylmethacrylate (PMMA) is added into the spiro‐OMeTAD matrix to improve the film formation process and hence the device performance. It is observed that, after modification, the spiro‐OMeTAD‐based hole‐transporting layer becomes uniform, continuous, and condensed. Meanwhile, the power conversion efficiency of the devices is upgraded. Compared with the control device, open‐circuit voltage of the modified one (with moderate doping) increases from 1.06 (±0.03) to 1.10 (±0.02) V, fill factor increases from 72.20 (±3.44)% to 75.59 (±3.35)%, and the power conversion efficiency increases from 18.82 (±1.06)% to 20.51 (±0.82)% (highest at 21.78%) under standard test condition (AM 1.5G, 100 mW cm−2). Transient photocurrent/photovoltage decay curves, time‐resolved photoluminance, and impedance spectroscopy studies show that the modification could accelerate charge transfer and retard interfacial recombination. In addition, the modification improves device stability. Due to the strengthened barrier against penetration of “H2O/O2/Ag,” the efficiency of the unsealed device could retain 91.49% (by average) of the initial one after 100 days storage in the dark [relative humidity = 30(±5)%]. This work shows that long‐chain polymer doping could simultaneously improve efficiency and stability of spiro‐OMeTAD‐based PSCs.
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Capsaicin is used to modify SnO 2 quantum dots and then used as an electron-transfer material for perovskite solar cells. After capsaicin modification, the power conversion efficiency of the devices increases from 19.90 (± 0.47)% to 21.87 (± 0.28)% with a champion device of 22.24% (AM 1.5G, 100 mW/cm 2 ). Transient photovoltage and photocurrent decay show that, after the capsaicin doping, the lifetime increases from 21.55 (± 1.54) to 27.63 (± 1.45) μs, while the charge extraction time reduces from 1.90 (± 0.09) to 1.67 (± 0.06) μs. Time-resolved photoluminescence and impedance spectrum studies show similar results. The accelerated charge transfer and retarded recombination are due to defect passivation. Space charge limited current study shows that, after modification, the trap density of devices is reduced from 2.24 × 10 15 to 1.28 × 10 15 cm −3 . X-ray photoelectron spectroscopy and theoretical calculation indicate that the reduced trap density is due to the chemical interaction between carbonyl group (from capsaicin) and Sn atom, and that between carbonyl group and Pb atom.more » « less
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Abstract A major challenge for graphene applications is the lack of mass production technology for large‐scale and high‐quality graphene growth and transfer. Here, a roll‐to‐roll (R2R) dry transfer process for large‐scale graphene grown by chemical vapor deposition is reported. The process is fast, controllable, and environmentally benign. It avoids chemical contamination and allows the reuse of graphene growth substrates. By controlling tension and speed of the R2R dry transfer process, the electrical sheet resistance is achieved as 9.5 kΩ sq−1, the lowest ever reported among R2R dry transferred graphene samples. The R2R dry transferred samples are used to fabricate graphene‐based field‐effect transistors (GFETs) on polymer. It is demonstrated that these flexible GFETs feature a near‐zero doping level and a gate leakage current one to two orders of magnitude lower than those fabricated using wet‐chemical etched graphene samples. The scalability and uniformity of the R2R dry transferred graphene is further demonstrated by successfully transferring a 3 × 3 in2sample and measuring its field‐effect mobility with 36 millimeter‐scaled GFETs evenly spaced on the sample. The field‐effect mobility of the R2R dry transferred graphene is determined to be 205 ± 36 cm2 V−1.
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Abstract Tailoring the doping of semiconductors in heterojunction solar cells shows tremendous success in enhancing the performance of many types of inorganic solar cells, while it is found challenging in perovskite solar cells because of the difficulty in doping perovskites in a controllable way. Here, a small molecule of 4,4′,4″,4″′‐(pyrazine‐2,3,5,6‐tetrayl) tetrakis (
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Accepted Manuscript1.0
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