It is been widely reported that plasmonic effects in metallic nanomaterials can enhance light trapping in organix solar cells (OSCs). However, typical nanoparticles (NP) of high quality (i.e., mono‐dispersive) only possess a single resonant absorption peak, which inevitably limits the power conversion efficiency (PCE) enhancement to a narrow spectral range. Broadband plasmonic absorption is obviously highly desirable. In this paper, a combination of Ag nanomaterials of different shapes, including nanoparticles and nanoprisms, is proposed for this purpose. The nanomaterials are synthesized using a simple wet chemical method. Theoretical and experimental studies show that the origin of the observed PCE enhancement is the simultaneous excitation of many plasmonic low‐ and high‐order resonances modes, which are material‐, shape‐, size‐, and polarization‐dependent. Particularly for the Ag nanoprisms studied here, the high‐order resonances result in higher contribution than low‐order resonances to the absorption enhancement of OSCs through an improved overlap with the active material absorption spectrum. With the incorporation of the mixed nanomaterials into the active layer, a wide‐band absorption improvement is demonstrated and the short‐circuit photocurrent density (Jsc) improves by 17.91%. Finally, PCE is enhanced by 19.44% as compared to pre‐optimized control OSCs. These results suggest a new approach to achieve higher overall enhancement through improving broadband absorption.

It is widely accepted that surface enhanced Raman scattering (SERS) enhancement results from a combination of electromagnetic mechanisms (EM) and chemical mechanisms (CM). Recently, the nanoparticle-fi lm gap (NFG) system was studied due to its strong local enhancement fi eld. However, there are still some technical limitations in establishing effective and simple ways for reliable and precise control of sub-nanospacer. In addition, works on designing the nanospacer in NFG system for effi cient interaction with target molecules for further improving SERS signals are rather limited. Here, a novel NFG system is proposed by introducing ultrathin monolayer graphene as well-defi ned subnanospacer between Ag NPs and Ag fi lm (named G(graphene)-NFG system). The new G-NFG system offers tremendous near-fi eld enhancement with one of the highest enhancement ratio of 1700 reported to date. These results show that the single-layer graphene as a sub-nanospacer renders the proposed G-NFG system with particularly strong EM enhancement (due to multiple couplings including the NP-NP couplings and NP-fi lm couplings) and additional CM enhancement in detecting some π-conjugated molecules to function as a powerful tool in analytical science and the related fi elds.

Recently, metal nanowires have received great research interests due to their potential as next-generation flexible transparent electrodes. While great efforts have been devoted to develop enabling nanowire electrodes, reduced contact resistance of the metal nanowires and improved electrical stability under continuous bias operation are key issues for practical applications. Here, we propose and demonstrate an approach through a low-cost, robust, room temperature and room atmosphere process to fabricate a conductive silver nano-network comprising silver nanowires and silver nanoparticles. To be more specific, silver nanoparticles are selectively grown and chemically integrated in situ at the junction where silver nanowires meet. The site-selective growth of silver nanoparticles is achieved by a plasmon-induced chemical reaction using a simple light source at very low optical power density. Compared to silver nanowire electrodes without chemical treatment, we observe tremendous conductivity improvement in our silver nano-networks, while the loss in optical transmission is negligible. Furthermore, the silver nano-networks exhibit superior electrical stability under continuous bias operation compared to silver nanowire electrodes formed by thermal annealing. Interestingly, our silver nano-network is readily peeled off in water, which can be easily transferred to other substrates and devices for versatile applications. We demonstrate the feasibly transferrable silver conductive nano-network as the top electrode in organic solar cells. Consequently, the transparent and conductive silver nano-networks formed by our approach would be an excellent candidate for various applications in optoelectronics and electronics.

4211wileyonlinelibrary.com spin-coater are generally adopted for coating the silver nanowires on specifi c substrate. [13][14][15][16][17] However, the as-formed silver nanowire electrode would exhibit poor conductive and stability performances because of their large contact resistance. [ 18 ] The coating of additional material on silver nanowire fi lm, such as poly (3,4-ethylenedioxythiophene):polysty rene sulfonate (PEDOT:PSS), TiO 2 , ZnO, graphene, graphene oxide, carbon nanotube, etc., for welding the silver nanowires has been recently reported, [19][20][21][22][23][24][25][26][27][28] which will however alter the work function of the nanowire electrodes. Previous welding approaches without introducing different material with the nanowires would involve the assistance of heat, electrical current, mechanical pressure, and light, [ 13,18,[29][30][31][32][33][34][35] which will have concerns to meet the broad requirements in the emerging fl exible optoelectronic fi eld. Therefore, forming highly stable and conductive silver nanowire transparent electrode adaptable for versatile electrode applications (both anode and cathode) through simple, low-cost, and time-saving approach at room temperature and ambient condition would be highly desirable.The application of silver nanowires in organic solar cell (OSC), with its effi ciency rapidly improved recently, [36][37][38][39][40][41][42][43][44][45][46] would greatly benefi t the realization of all solution processed, lowcost, and fl exible device. However, in previous reports, thin silver nanowires with diameter smaller than 30 nm have been selected and utilized for bottom electrodes of OSCs, [47][48][49][50][51][52] since nanowire fi lm with relatively small surface roughness can be easily fl attened by traditional interfacial materials. Although silver nanowires with larger diameter are much more thermally and chemically stable, fewer studies have focused on their usage (e.g. 100 nm in diameter), as the increased surface roughness of the electrodes can lead to leakage current and deteriorated performance for thin fi lm optoelectronic devices if not properly addressed. Suppressing the surface roughness of nanowire electrodes with large diameter for practical optoelectronic device applications is still a challenging issue. At present, the methods reported for addressing the issue still involve mechanical pressing of silver nanowires or transferring silver nanowires into polymer matrix. [53][54][55] Developing simple and Locally Welded Silver Nano-Network Transparent Electrodes with High Operational Stability by a Simple Alcohol-Based Chemical ApproachHaifei Lu , Di Zhang , Jiaqi Cheng , Jian Liu , Jian Mao , and Wallace C. H . Choy *As an indispensable aspect of emerging fl exible optoelectronics, fl exible transparent electrodes, especially those comprised of metal nanowires, have attracted great attentions recently. Welding the nanowire junctions is an effective strategy for reducing the sheet resistance and improving the operational stability of fl exible nanowire...

We report the first-order and high-order Raman scattering from core-shell CdSe/CdS nanocrystals and investigate the evolution of the longitudinal mode of CdSe (LO1) and CdS (LO2), and the surface mode of CdSe (SO1) and CdS (SO2) with increasing shell thickness (0-5.5 ML (monolayer)). We find that the shift of the LO2 peak from 268 to 291 cm(-1) agrees well with the theoretical values based on the phonon confinement model. The variation of the dielectric environment of the CdSe core with increasing CdS shell thickness is modified according to the shift of SO1 from 198 to 185 cm(-1). The SO2 modes at 267 and 275 cm(-1), corresponding to the shell thickness 3.5 and 5.5 ML in CdSe/CdS nanocrystals, respectively, are also obtained for the first time in our experiment. Moreover, they agree well with the theoretical values of the dielectric corresponding function model. Besides, a new Raman peak at 482 cm(-1) is observed, and it remains at that value with shell growth, the new peak is supposed to be caused by the alloying at the core-shell interface. Therefore, Raman spectroscopy can be used to determine the shell thickness and other surface and interface parameters of CdSe/CdS core-shell nanocrystals.

The exploration of low-temperature and solution-processed charge transporting and collecting layers can promote the development of low-cost and large-scale perovskite solar cells (PVSCs) through an all solution process. Here, we propose a room-temperature solution-processed and metal oxide-free nano-composite composed of a silver nano-network and graphene oxide (GO) flawless film for the transparent bottom electrode of a PVSC. Our experimental results show that the amount of GO flakes play a critical role in forming the flawless anti-corrosive barrier in the silver nano-network through a self-assembly approach under ambient atmosphere, which can effectively prevent the penetration of liquid or gaseous halides and their corrosion against the silver nano-network underneath. Importantly, we simultaneously achieve good work function alignment and surface wetting properties for a practical bottom electrode by controlling the degree of reduction of GO flakes. Finally, flexible PVSC adopting the room-temperature and solution-processed nano-composite as the flexible transparent bottom electrode has been demonstrated on a polyethylene terephthalate (PET) substrate. As a consequence, the demonstration of our room-temperature solution-processed and metal oxide-free flexible transparent bottom electrode will contribute to the emerging large-area flexible PVSC technologies.

Emerging novel metal electrodes not only serve as the collector of free charge carriers, but also function as light trapping designs in photovoltaics. As a potential alternative to commercial indium tin oxide, transparent electrodes composed of metal nanowire, metal mesh, and ultrathin metal film are intensively investigated and developed for achieving high optical transmittance and electrical conductivity. Moreover, light trapping designs via patterning of the back thick metal electrode into different nanostructures, which can deliver a considerable efficiency improvement of photovoltaic devices, contribute by the plasmon-enhanced light-mattering interactions. Therefore, here the recent works of metal-based transparent electrodes and patterned back electrodes in photovoltaics are reviewed, which may push the future development of this exciting field.

For ideal flexible transparent electrodes, the features of good electrical/ optical properties, low surface roughness, efficient charge transportation, robust electrical stability under simultaneously continuous operation bias, and mechanical bending are critical. Herein, a flexible transparent electrode fulfilling all these features is demonstrated by silver (Ag) nanonetwork composites semi-embedded in low-temperature-processed colorless polyimide (cPI), which shows a figure of merit over 1000 (5.4 Ω sq −1 sheet resistance and >94% diffused transmission at 550 nm wavelength), extremely smooth topography (<1 nm root-mean-square roughness and <3 nm peak-to-valley roughness), remarkable bending stability under continuous operation bias, and increased work function favoring the band alignment with typical charge transport layers for efficient devices. These characteristics are attributed to one-step multifunctional chemical treatment on the composite of Ag nanowires and an example polymer of poly(3,4-ethylenedioxythiophene):polysty rene sulfonate (PEDOT:PSS). The strategic one-step process simultaneously offers selective welding at nanowires cross junctions to form an Ag nanonetwork, and removing polyvinylpyrrolidone surfactant from Ag nanowires and PSS from PEDOT:PSS. The flexible electrode also favors the residue-free cPI transfer for applications. Flexible organic solar cells (OSCs) made from the electrode achieve an averaged power conversion efficiency of 14.46% (best, 15.12%), which is the best flexible OSCs reported so far.