by Alice Corani, Ming-Hsien Li, Po-Shen Shen, Peter Chen, Tzung-Fang Guo, Amal El Nahhas, Kaibo Zheng, Arkady Yartsev, Villy Sundström and Carlito S. Ponseca
Publication date: April 2016 Source:Nano Energy, Volume 22 Author(s): Segeun Jang, Jungjin Yoon, Kyungyeon Ha, Min-cheol Kim, Dong Hoe Kim, Sang Moon Kim, Seong Min Kang, Sei Jin Park, Hyun Suk Jung, Mansoo Choi The capability of fabricating three dimensional (3-D) nanostructures with desired morphology is a key to realizing effective light-harvesting strategy in optical applications. In this work, we report a novel 3-D nanopatterning technique that combines ion-assisted aerosol lithography (IAAL) and soft lithography that serves as a facile method to fabricate 3-D nanostructures. Aerosol nanoparticles can be assembled into desired 3-D nanostructures via ion-induced electrostatic focusing and antenna effects from charged nanoparticle structures. Replication of the structures with a polymeric mold allows high throughput fabrication of 3-D nanostructures with various liquid-soluble materials. 3-D flower-patterned polydimethylsiloxane (PDMS) stamp was prepared using the reported technique and utilized for fabricating 3-D nanopatterned mesoporous TiO2 layer, which was employed as the electron transport layer in perovskite solar cells. By incorporating the 3-D nanostructures, absorbed photon-to-current efficiency of >95% at 650nm wavelength and overall power conversion efficiency of 15.96% were achieved. The enhancement can be attributed to an increase in light harvesting efficiency in a broad wavelength range from 400 to 800nm and more efficient charge collection from enlarged interfacial area between TiO2 and perovskite layers. This hybrid nanopatterning technique has demonstrated to be an effective method to create textures that increase light harvesting and charge collection with 3-D nanostructures in solar cells.
Publication date: April 2016 Source:Nano Energy, Volume 22 Author(s): Hua Wang, Gaoyang Gou, Ju Li Perovskite ferroelectric materials exhibit the novel ferroelectric photovoltaic effect, where photon-excited electron–hole pairs can be separated by ferroelectric polarization. Especially, semiconducting ferroelectric materials with small band gaps ( E g ) have been extensively studied for applications in solar energy conversion. Traditional route for creating semiconducting ferroelectrics requires cation doping, where E g of the insulating perovskite ferroelectric oxides are reduced via substitution of certain cations. But cation doping tends to reduce the carrier mobility due to the scattering, and usually lead to poor photovoltaic efficiency. In the present work, based on first-principles calculations, we propose and demonstrate a new strategy for designing stoichiometric semiconducting perovskite ferroelectric materials. Specifically, we choose the parent non-polar semiconducting perovskite sulfides AB S 3 with Pnma symmetry, and turn them into ferroelectric Ruddlesden–Popper A 3 B 2 S 7 perovskites with spontaneous polarizations. Our predicted Ruddlesden–Popper Ca 3 Zr 2 S 7 and other derived compounds exhibit the room-temperature stable ferroelectricity, small band gaps ( E g < 2.2 eV ) suitable for the absorption of visible light, and large visible-light absorption exceeding that of Si.
Mater. Horiz., 2016, 3,220-225 DOI: 10.1039/C6MH00025H, Communication
Can Wang, Bingjia Xu, Mengshu Li, Zhenguo Chi, Yujun Xie, Qianqian Li, Zhen Li Two crystalline polymorphs of TMPE (Cp-form and Cc-form) exhibit totally different mechanoluminescence properties. The content of this RSS Feed (c) The Royal Society of Chemistry
Publication date: April 2016 Source:Nano Energy, Volume 22 Author(s): Zhibin Yang, Chu-Chen Chueh, Po-Wei Liang, Michael Crump, Francis Lin, Zonglong Zhu, Alex K.-Y. Jen Compositional engineering of organic-inorganic hybrid perovskite has attracted great research interests recently for seeking a better perovskite system to address existed challenges, such as the thermal and moisture instability, anomalous hysteresis, and toxic lead contamination, etc. In this study, we systematically investigated the structural, optophysical, and photovoltaic properties of the compositional MA x FA1−x Pb(I y Br1−y )3 perovskite by sequentially introducing FA+ and Br- ions into the parental MAPbI3 to elucidate their respective roles when they were inserted into the perovskite lattice. We unraveled that such dual compositional tuning in perovskite can improve the crystallinity of the resultant film and thus reduce its density of defect states as evidenced by admittance spectroscopy, resulting in a prolonged carrier lifetime over 500ns. As a result, a promising average PCE (PCEAVG) of 17.34% was realized in the optimized MA0.7FA0.3Pb(I0.9Br0.1)3-based PVSC with little hysteresis and stable photocurrent output. More significantly, another compositional MA0.7FA0.3Pb(I0.8Br0.2)3 perovskite with a large bandgap of 1.69eV can yield an impressively high PCEAVG over 15%. To the best of our knowledge, this performance is among the state-of-the-art large bandgap (~1.7eV) PVSCs reported so far, which paves the way for the development of high-performance tandem cells using efficient large bandgap PVSCs as the top subcells. This study not only manifests the pivotal roles of dual compositional tuning in MA x FA1−x Pb(I y Br1−y )3 perovskites but also highlights the importance of compositional engineering for developing an even more efficient perovskite.
Publication date: April 2016 Source:Nano Energy, Volume 22 Author(s): Miao Zhang, Fujun Zhang, Qiaoshi An, Qianqian Sun, Wenbin Wang, Jian Zhang, Weihua Tang Ternary strategy exhibits some apparent advantages to improve the performance of polymer solar cells (PSCs), such as using two donors or two acceptors to enhance photon harvesting and maintain the simple cell fabrication process. The power conversion efficiency (PCE) of PSCs was increased from 4.89% to 5.54% by doping 4wt% SMPV1 into Si-PCPDTBT:PC71BM binary system. The PCE improvement should be attributed to the enhanced photon harvesting in the visible light range and optimized charge carrier transport by doping appropriate SMPV1 in the active layers. The champion PCE values were also increased from 4.89% to 5.73% or from 5.54% to 6.44% for binary or the optimized ternary PSCs by CHCl3 solvent vapor annealing treatment. The positive effect of appropriate SMPV1 doping ratio should be attributed to the efficient energy transfer from SMPV1 to Si-PCPDTBT and the more balanced charge carrier transport in the ternary active layers. The energy transfer from SMPV1 to Si-PCPDTBT can be clearly confirmed from the absorption, photoluminescence (PL) spectra and time-resolved transient PL spectra of pure and blend films. The more balanced charge carrier transport can be further demonstrated from the corresponding hole-only and electron-only devices.
Publication date: April 2016 Source:Nano Energy, Volume 22 Author(s): Haonan Si, Qingliang Liao, Zheng Zhang, Yong Li, Xuhui Yang, Guangjie Zhang, Zhuo Kang, Yue Zhang A novel perovskite solar cell (PSC) structure with high efficiency is designed through separating the ZnO electron transport layer and perovskite layer by an ultra-thin Al2O3 insulating layer. The application of insulating layer can effectively decline the degradation rate of perovskite. In addition, the thickness of the insulating layer is optimized by a quantum tunneling model based on effective-mass approximation (EMA) theory. The performance of the PSCs could be modulated by tuning the thickness of Al2O3 middle layer, and the experimental results are consistent with theoretical results. The optimal insulating layer has a capability to suppress the carriers recombination process and improve the conversion efficiency of PSCs. The highest conversion efficiency of optimized PSC is 15.55% at the thickness of 4Å. Therefore, the interface modulation protocol of inserting Al2O3 insulating layer at ZnO/perovskite interface provides a promising approach for novel design of PSCs with commercial values.
The high efficiency single-junction polymer solar cells (PSCs) are demonstrated by firstly incorporating two hyperbranched polymers (CHBPEK and SHBPES) with quasi-immovable counterions to modify the cathode interface. The device with SHBPES as cathode interlayer can be achieved with a highest PCE of 9.12% by the influence of interfacial dipole based on quasi-immovable counterions in these polymers.
Publication date: March 2016 Source:Nano Energy, Volume 21 Author(s): Zeguo Tang, Soichiro Tanaka, Seigo Ito, Shigeru Ikeda, Kozo Taguchi, Takashi Minemoto Methylammonium lead iodide (MAPbI3) perovskite solar cells are fabricated by two-step sequential deposition processes. The influence of the properties of PbI2 precursor film on the cell performance is investigated based on different solvents. The X-ray diffraction (XRD) patterns, Urbach energy value and scan electron microscope (SEM) images reveal that solvents have considerable influence on the crystal structure, band tail and morphology of PbI2 precursor films. The addition of a small amount of dimethyl sulfoxide (DMSO) in N,N-dimethylformamide (DMF) solvent promotes the compactness and uniformity of PbI2 precursor films, but also causes defect in band tail. The relation of the properties of perovskite film with photovoltaic parameters is explored. A high conversion efficiency of 16.6% for solar cells based on mixed solvents with 10vol% DMSO is achieved. Meanwhile, light beam-induced current (LBIC) images directly evidence the improvement of uniformity for perovskite solar cells caused by DMSO addition.
J. Mater. Chem. A, 2016, 4,1612-1623 DOI: 10.1039/C5TA09712F, Communication
Dimitrios Konios, George Kakavelakis, Costantinos Petridis, Kyriaki Savva, Emmanuel Stratakis, Emmanuel Kymakis Utilization of work-function (WF) tuned graphene oxide derivatives as cathode and anode buffer layers in organic photovoltaics (OPVs) is demonstrated. The content of this RSS Feed (c) The Royal Society of Chemistry
Publication date: April 2016 Source:Solar Energy Materials and Solar Cells, Volume 147 Author(s): Dian Wang, Matthew Wright, Naveen Kumar Elumalai, Ashraf Uddin The performance of perovskite solar cells has increased at an unprecedented rate, with efficiencies currently exceeding 20%. This technology is particularly promising, as it is compatible with cheap solution processing. For a thin-film solar product to be commercially viable, it must pass the IEC 61646 testing standards, regarding the environmental stability. Currently, the poor stability of perovskite solar cells is a barrier to commercialisation. The main issue causing this problem is the instability of the perovskite layer when in contact with moisture; however, it is important to explore stability problems with the other layers and interfaces within the device. The stability issues discussed in this review highlight the need to view the device as a whole system, due to the interdependent relationships between the layers, including: the perovskite absorber, electron transport layers, hole transport layers, other buffer layers and the electrodes. We also discuss other issues pertaining to device stability, such as measurement-induced hysteresis and the requirement for standard testing protocols. For perovskite solar cells to achieve the required stability, future research must focus on improving the intrinsic stability of the perovskite absorber layer, carefully designing the device geometry, and finding durable encapsulant materials, which seal the device from moisture.
J. Mater. Chem. A, 2016, 4,6755-6771 DOI: 10.1039/C5TA09661H, Review Article
Meidan Ye, Xiaodan Hong, Fayin Zhang, Xiangyang Liu This review focuses on the aspects of flexibility, stability and large scale, which are very essential for the future commercialization of PSCs, and many effective materials and fabrication strategies which have been reported to emphasize these three properties of PSCs will be introduced. The content of this RSS Feed (c) The Royal Society of Chemistry
by Shreyam Chatterjee, Yutaka Ie, Makoto Karakawa, Yoshio Aso
The development of nonfullerene acceptor materials applicable to organic photovoltaics (OPVs) has attracted considerable attention for the achievement of a high power conversion efficiency (PCE) in recent years. However, it is still challenging due to the insufficiency of both the variety of effective electron-deficient units and certain guidelines for the design of such materials. This work focusses on naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole (NTz) as a key electron-deficient unit. Therefore, a new electron-accepting π-conjugated compound (NTz-Np), whose structure is based on the combination of NTz and the fluorene-containing imide-annelated terminal units (Np), is designed and synthesized. The NTz-Np compound exhibits a narrow optical energy gap (1.73 eV), a proper energy level (−3.60 eV) of the lowest unoccupied molecular orbital, and moderate electron mobility (1.6 × 10−5 cm2 V−1 s−1), indicating that NTz-Np has appropriate characteristics as an acceptor against poly(3-hexylthiophene) (P3HT), a representative donor. OPV devices based on NTz-Np under the blend with P3HT show high photovoltaic performance with a PCE of 2.81%, which is the highest class among the P3HT/nonfullerene-based OPVs with the conventional device structure. This result indicates that NTz unit can be categorized as a potential electron-deficient unit for the nonfullerene acceptors.
An electron-accepting π-conjugated compound based on naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole is designed and synthesized as a nonfullerene acceptor material in organic photovoltaics. Photophysical and electrochemical measurements indicate that this compound has appropriate properties for photovoltaic application. Bulk-heterojunction solar cells using a blend film of P3HT and the synthesized acceptor as an active layer show photovoltaic characteristics with power conversion efficiencies of up to 2.81%.
by Jaewon Lee, Ranbir Singh, Dong Hun Sin, Heung Gyu Kim, Kyu Chan Song, Kilwon Cho
In the past few years, fullerene-free organic solar cells have become the focus of many research efforts. On page 69, K. Cho and co-workers report a new non-fullerene small-molecule acceptor that has 3D interlocking geometry, enabling a nanoscale and bicontinuous 3D network morphology in bulk-heterojunction organic solar cells. This work provides important guidance to design the material structure and improve the performance of non-fullerene organic solar cells.
J. Mater. Chem. A, 2015, Accepted Manuscript DOI: 10.1039/C5TA09712F, Communication
Dimitrios Konios, George Kakavelakis, Kyriaki Savva, Costas Petridis, Emmanuel Stratakis, Emmanuel Kymakis The effective utilization of work-function (WF) tuned solution processable graphene-based derivatives as both hole and electron transport layers in organic photovoltaic (OPV) devices is demonstrated. The systematic tuning of functionalized... The content of this RSS Feed (c) The Royal Society of Chemistry
by Alexander R. Pascoe, Steffen Meyer, Wenchao Huang, Wei Li, Iacopo Benesperi, Noel W. Duffy, Leone Spiccia, Udo Bach, Yi-Bing Cheng
Perovskite-based solar cells are generally assembled as planar structures comprising a flat organoammonium metal halide perovskite layer, or mesoscopic structures employing a mesoporous metal-oxide scaffold into which the perovskite material is infiltrated. To present, little attention has been directed toward the texturing of the perovskite material itself. Herein, a textured CH3NH3PbI3 morphology formed through a thin mesoporous TiO2 seeding layer and a gas-assisted crystallization method is reported. The textured morphology comprises a multitiered nanostructure, which allows for significant improvements in the light harvesting and charge extraction performance of the solar cells. Due to these improvements, average short-circuit current densities for a batch of 28 devices are in excess of 22 mA cm−2, and the maximum recorded power conversion efficiency is 16.3%. The performance gains concomitant with this textured CH3NH3PbI3 morphology provide further insights into how control of the perovskite microstructure can be used to enhance the cell performance.
A textured CH3NH3PbI3 morphology for perovskite-based solar cells is presented. The textured morphology exhibits enhanced light harvesting and charge separation properties. The highest measured power conversion efficiency is 16.3%.
by Chetan R. Singh, Cheng Li, Christian J. Mueller, Sven Hüttner, Mukundan Thelakkat
The influence of different electron extracting interlayers such as calcium (Ca), zirconium acetylacetonate (ZrAcac), and a polyfluorene derivative (PFN) in combination with an aluminum (Al) cathode is investigated on the performance of bulk-heterojuntion solar cells. Two different photoactive systems, P3HT:PC61BM and PDPP:PC71BM, are selected for this study. The electroabsorption measurements have been carried out for obtaining the built-in voltage (Vbi) and transfer matrix simulations for the determination of parasitic absorption. The solar cell performance is influenced by different parameters such as diode turn-on voltage, leakage currents, built-in voltages, and parasitic absorption. The small diode turn-on voltage and high parasitic absorption in Ca contact devices limit the open circuit voltage and short circuit current, respectively. Likewise, high leakage currents using ZrAcac contact limit the fill factor in P3HT:PC61BM solar cell devices. However, the PFN-based devices with small parasitic absorption, smaller leakage currents, and a relatively high Vbi show maximum performance with both material systems. This work highlights the importance of choosing the suitable interlayers in device optimization and clearly demonstrates that not only the low work function of an electron extracting interlayer but also its optical properties and charge selectivity significantly influence the final solar cell performance.
The influence of different electron extracting interlayers including Ca, ZrAcac, and PFN in combination with Al is investigated in normal organic solar cell geometry using electroabsorption measurements and transfer matrix simulations. It is shown that the solar cell performance is influenced by different parameters such as diode turn-on voltage, leakage currents, built-in voltages, and parasitic absorption.
Publication date: February 2016 Source:Nano Energy, Volume 20 Author(s): Fuguo Zhang, Xichuan Yang, Ming Cheng, Weihan Wang, Licheng Sun Low temperature printable carbon cathode based perovskite solar cell was for the first time interfacial engineered with dopant free, nanorod-liked copper phthalocyanine (CuPc) to facilitate charge transportation. Both the CuPc and low temperature processed carbon are potentially noble metal-free and highly stable. By incorporating CuPc nanorods as hole-selective contact material, together with the printable low temperature processed carbon as cathode material, considerably high power conversion efficiency (PCE) of 16.1% was successfully obtained, which is comparable to or even a little higher than the device with state-of-the-art doped spiro-OMeTAD as HTM and noble metal Au as back electrode. Moreover, dramatically enhanced durability relative to doped-spiro-OMeTAD/Au based device was demonstrated by this newly developed device. Detailed excellent capability in accelerating charge extraction and suppressing charge recombination can be disclosed with steady state and time-resolved photoluminescence analysis and electrochemical impedance spectroscopy. To the best our knowledge, this is the highest efficiency that has been reported for PSCs based carbon counter electrode. The work presented here demonstrates an important step forwards to practical applications for PSCs, as it paves the way for developments of cost-effective, stable but still highly efficient PSCs, and offers the promise for a low-cost, mass-manufacturable technology that is compatible with current large-scale printing infrastructure.
Publication date: February 2016 Source:Nano Energy, Volume 20 Author(s): Byung Joon Moon, Kyu Seung Lee, Jaeho Shim, Soohyung Park, Se Ho Kim, Sukang Bae, Min Park, Chang-Lyoul Lee, Won Kook Choi, Yeonjin Yi, Jun Yeon Hwang, Dong Ick Son Recently, interfacial engineering approaches as an efficient strategy for improving the power conversion efficiencies (PCEs) of inverted polymer solar cells (iPSCs) has attracted considerable attention. Among various efficient solutions, solution-processed metal-oxide films prepared from metal oxide sol–gel precursors (or nanoparticles) and polymer surface modifiers are typically used as electron selective interfaces in the inverted cell geometry. To present a more effective strategy for surpassing the limitations of traditional methods, such as an unintended increase in series or contact resistance by incompatibility at the organic/inorganic interface, inherently insulating nature of non-conjugated surface modifiers and oxygen adsorption (or photo-induced doping) of metal-oxide layer, we synthesize chemically surface-modified ZnO@graphene core–shell type quantum dots (ZGQDs) with well-characterization of the chemical, optical and electrical properties, and fabricate iPSCs consisting of ITO/PEIE/ZGQD-OAs/photoactive layer/MoO3/Ag. The mono-layered QDs play the multi-functional role as surface modifier, sub-photosensitizer and electron transport layer. Using this effective approach, we achieve the highest conversion efficiency of ~10.3% resulting from improved interfacial properties and efficient charge transfer based on static quenching and charge transfer reaction from ZnO to graphene nanosheets (with drastically reduced τavg (~ 60ps)), which is verified by various analysis tools.
J. Mater. Chem. A, 2016, 4,561-567 DOI: 10.1039/C5TA08262E, Paper
Yuanhang Cheng, Ho-Wa Li, Jinfeng Zhang, Qing-Dan Yang, Taili Liu, Zhiqiang Guan, Jian Qing, Chun-Sing Lee, Sai-Wing Tsang The loading time of MAI during perovskite film formation determines the chemical composition, hysteresis, and photovoltaic performance. The content of this RSS Feed (c) The Royal Society of Chemistry
by Elizabeth M. Tennyson, Joseph L. Garrett, Jesse A. Frantz, Jason D. Myers, Robel Y. Bekele, Jasbinder S. Sanghera, Jeremy N. Munday, Marina S. Leite
In article number 1501142, Marina S. Leite and co-workers report the use of an imaging platform to map open-circuit voltage in solar cells with a lateral spatial resolution of <100 nm that can be applied to any material. The cover illustration shows an atomic force microscopy (AFM) probe ‘in motion’, a reference to the illuminated in situ measurements.
