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Title: Improved moisture resistance and interfacial recombination of perovskite solar cells by doping oleylamine in spiro-OMeTAD based hole-transport layer
Hydrophobic and long-chain molecule oleylamine is used to modify the spiro-OMeTAD matrix, which is then adopted for the hole-transport layer in perovskite solar cells. It is observed that after moderate doping, the power conversion efficiency of the devices increases from 17.82 (±1.47)% to 20.68 (±0.77)%, with the optimized efficiency of 21.57% (AM 1.5G, 100 mW/cm2). The improved efficiency is ascribed to the favored charge extraction and retarded charge recombination, as reflected by transient photovoltage/photocurrent curves and impedance spectroscopy measurement. In addition, the grazing incidence photoluminescence spectrum reveals that oleylamine doping causes a blue shift of the luminescence peak of the surface layer of the halide perovskite film, while the Mott−Schottky study observes 100 mV increment in the built-in potential, both of which indicate possible defect passivation behavior on the perovskite. Moreover, an accelerated damp test observes that moisture resistance of the device is also upgraded, which is due to the improved hydrophobicity of the spiro-OMeTAD matrix.  more » « less
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Applied Physics Letters
Medium: X
Sponsoring Org:
National Science Foundation
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  2. Abstract

    Hole transport layer (HTL) is very important for the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). As current state‐of‐the‐art HTL, Li‐TFSI doped spiro‐OMeTAD often suffers low conductivity and the hydrolysis of the additive Li‐TFSI, which significantly hinders the further improvement of PCE of PSCs. Besides, conventional spiro‐OMeTAD has no functional of directly passivating the perovskite crystal defects. Herein, multifunctional TiO2nanoparticles (NPs)‐modified CNT (CNT:TiO2) doped spiro‐OMeTAD (spiro‐OMeTAD+CNT:TiO2) HTL is reported for the first time. The incorporated CNT:TiO2not only significantly increases the conductivity of spiro‐OMeTAD+CNT:TiO2, but also effectively passivates the crystal defects of perovskite layer. The optimized PSCs with spiro‐OMeTAD+CNT:TiO2HTL achieved a peak PCE of 21.53%, much higher than that (17.90%) of the conventional spiro‐OMeTAD based PSCs and also show significantly improved stability.image

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  3. null (Ed.)
    While typical perovskite solar cells (PSCs) with doped Spiro-OMeTAD as a hole transport material (HTM) have shown rapid increase in their power-conversion efficiencies (PCEs), their poor stability remains a big concern as the dopants and additives used with Spiro-OMeTAD have a strong tendency to diffuse into and degrade the perovskite active layer under normal operating conditions. Aiming to push forward the development of PSCs, many dopant-free small-molecular HTMs have been reported based on energetic considerations for charge transfer and criteria for charge transport. However, the PCEs of the state-of-the-art PSCs with dopant-free small-molecular HTMs are still inferior to those using doped Spiro-OMeTAD, and little attention has been paid to the interactions between the HTM and perovskite absorber in PSCs. Here, we report a facile design concept to functionalize HTMs so that they can passivate perovskite surface defects and enable perovskite active layers with lower density of surface trap states and more efficient charge transfer to the hole transport layer. As a consequence, perovskite solar cells with a functionalized HTM exhibit a champion PCE of 22.4%, the highest value for PSCs using dopant-free small molecular HTMs to date, and substantively improved operational stability under continuous illumination. With a T 80 of (1617 ± 7) h for encapsulated cells tested at 30 °C in air, the PSCs containing the functionalized HTM are among the most stable PSCs using dopant-free small-molecular HTMs. The effectiveness of our strategy is demonstrated in PSCs comprising both a state-of-the-art MA-free perovskite and MAPbI, a system having more surface defects, and implies the potential generality of our strategy for a broad class of perovskite systems, to further advance highly efficient and stable solar cells. 
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  4. Abstract

    Tri‐cation (Cs+/CH3NH3+/CH(NH2)2+) and dual‐anion (Br/I) perovskites are promising light absorbers for inexpensive infrared (IR) photodetectors but degrade under prolonged IR exposure. Here, stable IR photodetectors based on electrospun tri‐cation perovskite fibers infiltrated with hole‐transporting π‐conjugated small molecule 2,2′,7,7′‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9,9‐spirobifluorene (Spiro‐OMeTAD) are demonstrated. These hybrid perovskite photodetectors operate at a low bias of 5 V and exhibit ultra‐high gains with external quantum efficiencies (EQEs) as high as 3009%, decreasing slightly to ≈2770% after 3 months in air. These EQE values are almost ten times larger than those measured for photodetectors comprising bilayer perovskite/Spiro‐OMeTAD films. A high density of charge traps on electrospun fiber surfaces gives rise to a photomultiplication effect in which photogenerated holes can travel through the active layer multiple times before recombining with trapped electrons. Time‐resolved photoluminescence and conductive atomic force microscopy mapping reveal the improved performance of electrospun fibers to originate from the significantly enhanced interfacial surface area between the perovskite and Spiro‐OMeTAD compared to bilayers. As a solution‐based, scalable and continuous method of depositing perovskite layers, electrospinning thus presents a promising strategy for the inexpensive fabrication of high‐performance IR photodetectors for applications ranging from information technology to imaging.

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    Flexible perovskite solar cells (f‐PSCs) have attracted great attention due to their promising commercial prospects. However, the performance off‐PSCs is generally worse than that of their rigid counterparts. Herein, it is found that the unsatisfactory performance of planar heterojunction (PHJ)f‐PSCs can be attributed to the undesirable morphology of electron transport layer (ETL), which results from the rough surface of the flexible substrate. Precise control over the thickness and morphology of ETL tin dioxide (SnO2) not only reduces the reflectance of the indium tin oxide (ITO) on polyethylene 2,6‐naphthalate (PEN) substrate and enhances photon collection, but also decreases the trap‐state densities of perovskite films and the charge transfer resistance, leading to a great enhancement of device performance. Consequently, thef‐PSCs, with a structure of PEN/ITO/SnO2/perovskite/Spiro‐OMeTAD/Ag, exhibit a power conversion efficiency (PCE) up to 19.51% and a steady output of 19.01%. Furthermore, thef‐PSCs show a robust bending resistance and maintain about 95% of initial PCE after 6000 bending cycles at a bending radius of 8 mm, and they present an outstanding long‐term stability and retain about 90% of the initial performance after >1000 h storage in air (10% relative humidity) without encapsulation.

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