Fine Multi-Phase Alignments in 2D Perovskite Solar Cells with Efficiency over 17% via Slow Post-Annealing.

Layered Ruddlesden-Popper (RP) phase (2D) halide perovskites have attracted tremendous attention due to the wide tunability on their optoelectronic properties and excellent robustness in photovoltaic devices. However, charge extraction/transport and ultimate power conversion efficiency (PCE) in 2D perovskite solar cells (PSCs) are still limited by the non-eliminable quantum well effect. Here, a slow post-annealing (SPA) process is proposed for BA2 MA3 Pb4 I13 (n = 4) 2D PSCs by which a champion PCE of 17.26% is achieved with simultaneously enhanced open-circuit voltage, short-circuit current, and fill factor. Investigation with optical spectroscopy coupled with structural analyses indicates that enhanced crystal orientation and favorable alignment on the multiple perovskite phases (from the 2D phase near bottom to quasi-3D phase near top regions) is obtained with SPA treatment, which promotes carrier transport/extraction and suppresses Shockley-Read-Hall charge recombination in the solar cell. As far as it is known, the reported PCE is so far the highest efficiency in RP phase 2D PSCs based on butylamine (BA) spacers (n = 4). The SPA-processed devices exhibit a satisfactory stability with <4.5% degradation after 2000 h under N2 environment without encapsulation. The demonstrated process strategy offers a promising route to push forward the performance in 2D PSCs toward realistic photovoltaic applications.

Interfacial Modification in Organic and Perovskite Solar Cells.

Organic bulk heterojunction solar cells (OSCs) and hybrid halide perovskite solar cells (PSCs) are two promising photovoltaic techniques for next-generation energy conversion devices. The rapid increase in the power conversion efficiency (PCE) in OSCs and PSCs has profited from synergetic progresses in rational material synthesis for photoactive layers, device processing, and interface engineering. Interface properties in these two types of devices play a critical role in dictating the processes of charge extraction, surface trap passivation, and interfacial recombination. Therefore, there have been great efforts directed to improving the solar cell performance and device stability in terms of interface modification. Here, recent progress in interfacial doping with biopolymers and ionic salts to modulate the cathode interface properties in OSCs is reviewed. For the anode interface modification, recent strategies of improving the surface properties in widely used PEDOT:PSS for narrowband OSCs or replacing it by novel organic conjugated materials will be touched upon. Several recent approaches are also in focus to deal with interfacial traps and surface passivation in emerging PSCs. Finally, the current challenges and possible directions for the efforts toward further boosts of PCEs and stability via interface engineering are discussed.

Retardation of Trap-Assisted Recombination in Lead Halide Perovskite Solar Cells by a Dimethylbiguanide Anchor Layer.

Reaching the full potential of solar cells based on photo-absorbers of organic-inorganic hybrid perovskites requires highly efficient charge extraction at the interface between perovskite and charge transporting layer. This demand is generally challenged by the presence of under-coordinated metal or halogen ions, causing surface charge trapping and resultant recombination losses. These problems can be tackled by introducing a small molecule interfacial anchor layer based on dimethylbiguanide (DMBG). Benefitting from interactions between the nitrogen-containing functional groups in DMBG and unsaturated ions in CH3 NH3 PbI3 perovskites, the electron extraction of TiO2 is dramatically improved in association with reduced Schottky-Read-Hall recombination, as revealed by photoluminescence spectroscopy. As a consequence, the power conversion efficiency of CH3 NH3 PbI3 solar cells is boosted from 17.14 to 19.1 %, showing appreciably reduced hysteresis. The demonstrated molecular strategy based on DMBG enables one to achieve meliorations on key figures of merit in halide perovskite solar cells with improved stability.

Incorporating an Inert Polymer into the Interlayer Passivates Surface Defects in Methylammonium Lead Halide Perovskite Solar Cells.

The hysteresis effect and instability are important concerns in hybrid perovskite photovoltaic devices that hold great promise in energy conversion applications. In this study, we show that the power conversion efficiency (PCE), hysteresis, and device lifetime can be simultaneously improved for methylammoniumlead halide (CH3 NH3 PbI3-x Clx ) solar cells after incorporating poly(methyl methacrylate) (PMMA) into the PC61 BM electron extraction layer (EEL). By choosing appropriate molecular weights of PMMA, we obtain a 30 % enhancement of PCE along with effectively lowered hysteresis and device degradation, adopting inverted planar device structure. Through the combinatorial study using Kelvin probe force microscopy, diode mobility measurements, and irradiation-dependent solar cell characterization, we attribute the enhanced device parameters (fill factor and open circuit voltage) to the surface passivation of CH3 NH3 PbI3-x Clx , leading to mitigating charge trapping at the cathode interface and resultant Shockley-Read-Hall charge recombination. Beneficially, modified by inert PMMA, CH3 NH3 PbI3-x Clx solar cells display a pronounced retardation in performance degradation, resulting from improved film quality in the PC61 BM layer incorporating PMMA which increases the protection for underneath perovskite films. This work enables a versatile and effective interface approach to deal with essential concerns for solution-processed perovskite solar cells by air-stable and widely accessible materials.

Synthesis of graphene and related two-dimensional materials for bioelectronics devices.

In recent years, graphene and related two-dimensional (2D) materials have emerged as exotic materials in nearly every fields of fundamental science and applied engineering. The latest progress has shown that these 2D materials could have a profound impact on bioelectronics devices. For the construction of these bioelectronics devices, these 2D materials were generally synthesized by the processes of exfoliation and chemical vapor deposition. In particular, the macrostructures of these 2D materials have also been realized by these two processes, which have shown great potentials in the self-supported and special-purpose biosensors. Due to the high specific surface area, subtle electron properties, abundant surface atoms of these 2D materials, the as-constructed bioelectronics devices have exhibited enhanced performance in the sensing of small biomolecules, heavy metals, pH, protein and DNA. The aim of this review article is to provide a comprehensive scientific progress in the synthesis of 2D materials for the construction of five typical bioelectronics devices (electrochemical biosensors, FET-based biosensors, piezoelectric devices, electrochemiluminescence devices and supercapacitors) and to overview the present status and future perspective of the applications of these bioelectronics devices based on 2D materials.

3D nitrogen-doped graphene/ß-cyclodextrin: host-guest interactions for electrochemical sensing.

Host-guest interactions, especially those between cyclodextrins (CDs, including α-, ß- and γ-CD) and various guest molecules, exhibit a very high supramolecular recognition ability. Thus, they have received considerable attention in different fields. These specific interactions between host and guest molecules are promising for biosensing and clinical detection. However, there is a lack of an ideal electrode substrate for CDs to increase their performance in electrochemical sensing. Herein, we propose a new 3D nitrogen-doped graphene (3D-NG) based electrochemical sensor, taking advantage of the superior sensitivity of host-guest interactions. Our 3D-NG was fabricated by a template-directed chemical vapour deposition (CVD) method, and it showed a large specific surface area, a high capacity for biomolecules and a high electron transfer efficiency. Thus, for the first time, we took 3D-NG as an electrode substrate for ß-CD to establish a new type of biosensor. Using dopamine (DA) and acetaminophen (APAP) as representative guest molecules, our 3D-NG/ß-CD biosensor shows extremely high sensitivities (5468.6 µA mM(-1) cm(-2) and 2419.2 µA mM(-1) cm(-2), respectively), which are significantly higher than those reported in most previous studies. The stable adsorption of ß-CD on 3D-NG indicates potential applications in clinical detection and medical testing.