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- Wang, Zheng, et al.
(författare)
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Trade-off effect of hydrogen-bonded dopant-free hole transport materials on performance of inverted perovskite solar cells
- 2024
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Ingår i: Nano Energy. - 2211-2855. ; 128
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Tidskriftsartikel (refereegranskat)abstract
- Benefiting from their ordered orientation and superior stability compared to traditional conjugated materials, hydrogen bonding (HB)-induced H-aggregates in organic small molecule hole-transport materials (HTMs) hold a big potential for high-performance inverted perovskite solar cells (IPSCs). However, H-aggregates can also lead to excessive face-aggregation by forming the gaps between aggregates, which is in turn unfavorable for charge mobility and thus for the overall device performance. Herein, we design and synthesize a new set of HB-containing triphenylamine-based small molecules to tailor the degree of H-aggregation, namely O1 (without HB), O2 (unilateral HB unit), and O3 (bilateral HB units). These HTMs make a clear trade-off effect on the charge mobility within the HTM and the interfacial properties of perovskite and HTM. Although the interfacial hole extraction process is promoted upon the HB-functionalized interface, the best performance of IPSCs is still achieved by O1 HTM, which is mainly influenced by the higher hole mobility without HB-induced H-aggregates. Nevertheless, the photo stability of as-fabricated devices is effectively improved upon the HB passivation effect on the interface of HTM (O2 or O3) and perovskite, as well as the better quality of atop perovskite layers with less grain boundary compared to the reference case (O1).
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| 4. |
- Gao, Yipeng, et al.
(författare)
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Research on the Security of Visual Reasoning CAPTCHA
- 2021
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Ingår i: PROCEEDINGS OF THE 30TH USENIX SECURITY SYMPOSIUM. - : USENIX ASSOC. - 9781939133243 ; , s. 3291-3308
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Konferensbidrag (refereegranskat)abstract
- CAPTCHA is an effective mechanism for protecting computers from malicious bots. With the development of deep learning techniques, current mainstream text-based CAPTCHAs have been proven to be insecure. Therefore, a major effort has been directed toward developing image-based CAPTCHAs, and image-based visual reasoning is emerging as a new direction of such development. Recently, Tencent deployed the Visual Turing Test (VTT) CAPTCHA. This appears to have been the first application of a visual reasoning scheme. Subsequently, other CAPTCHA service providers (Geetest, NetEase, Dingxiang, etc.) have proposed their own visual reasoning schemes to defend against bots. It is, therefore, natural to ask a fundamental question: are visual reasoning CAPTCHAs as secure as their designers expect? This paper presents the first attempt to solve visual reasoning CAPTCHAs. We implemented a holistic attack and a modular attack, which achieved overall success rates of 67.3% and 88.0% on VTT CAPTCHA, respectively. The results show that visual reasoning CAPTCHAs are not as secure as anticipated; this latest effort to use novel, hard AI problems for CAPTCHAs has not yet succeeded. Based on the lessons we learned from our attacks, we also offer some guidelines for designing visual CAPTCHAs with better security.
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| 5. |
- Li, Rui, et al.
(författare)
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Twisted or Planar? Side-Chain Tailoring of Fluorene-based Hole-Transport Materials for Efficient and Stable Perovskite Solar Cells
- 2023
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Ingår i: Solar RRL. - 2367-198X. ; 7:18
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Tidskriftsartikel (refereegranskat)abstract
- The functionalization of small-molecule hole-transport materials (HTMs) heavily relies on the rational design of molecular geometry, which can optimize both intrinsic HTM properties and interfacial properties for realizing high-performance and stable lead halide perovskite solar cells (LHPSCs). Herein, two fluorene-based donor–π linker–donor HTMs are seen, FL01 and FL02, whose side chains are tailored with planar phenyl-carbazole groups and twisted triphenylamine groups, respectively. Benefiting from the high conformational flexibility of twisted side chains, the strong and oriented interaction via PbO bonding is well coordinated at the perovskite and FL02 interface, which favors the interfacial charge transfer as well as the protection of perovskite layer by effectively blocking or mitigating the diffusion of hygroscopic dopants toward the perovskite surface. Consequently, the performance of FL02 HTM-based n–i–p LHPSCs is significantly enhanced by achieving a power conversion efficiency of 17.8%, which is twice higher than that (8.6%) of FL01 HTM-based ones and comparable with the case (18.8%) of conventional spiro-OMeTAD HTM-based devices. More importantly, the FL02-based devices exhibit impressively high operation and storage stabilities with T80 and TS80 lifetimes of >98 h and ≈270 days, respectively, which are among the longest lifespans for the type of hygroscopically doped LHPSCs.
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