Unveiling the operation mechanism of layered perovskite solar cells

Layered perovskites have been shown to improve the stability of perovskite solar cells while its operation mechanism remains unclear. Here we investigate the process for the conversion of light to electrical current in high performance layered perovskite solar cells by examining its real morphology. The layered perovskite films in this study are found to be a mixture of layered and three dimensional (3D)-like phases with phase separations at micrometer and nanometer scale in both vertical and lateral directions. This phase separation is explained by the surface initiated crystallization process and the competition of the crystallization between 3D-like and layered perovskites. We further propose that the working mechanisms of the layered perovskite solar cells involve energy transfer from layered to 3D-like perovskite network. The impact of morphology on efficiency and stability of the hot-cast layered perovskite solar cells are also discussed to provide guidelines for the future improvement

A new Scanning Transmission X-ray Microscope at the ALS for operation up to 2500eV

We report on the design and construction of a higher energy Scanning Transmission X-ray Microscope on a new bend magnet beam line at the Advanced Light Source. Previously we have operated such an instrument on a bend magnet for C, N and O 1s NEXAFS spectroscopy. The new instrument will have similar performance at higher energies up to and including the S 1s edge at 2472eV. A new microscope configuration is planned. A more open geometry will allow a fluorescence detector to count emitted photons from the front surface of the sample. There will be a capability for zone plate scanning in addition to the more conventional sample scanning mode. This will add the capability for imaging a massive sample at high resolution over a limited field of view, so that heavy reaction cells may be used to study processes in-situ, exploiting the longer photon attenuation length and the longer zone plate working distances available at higher photon energy. The energy range will extend down to include the C1s edge at 300eV, to allow high energy NEXAFS microscopic studies to correlate with the imaging of organics in the same sample region of interest

Erratum: A multi-objective optimization-based layer-by-layer blade-coating approach for organic solar cells: Rational control of vertical stratification for high performance (Energy and Environmental Science (2019) 12 (3118-3132) DOI: 10.1039/C9EE02295C)

The Acknowledgements section should have included the following sentence: "This work was performed in part on the SAXS/ WAXS beamline at the Australian Synchrotron, part of ANSTO". The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers

A multi-objective optimization-based layer-by-layer blade-coating approach for organic solar cells:Rational control of vertical stratification for high performance

A major breakthrough in organic solar cells (OSCs) in the last thirty years was the development of the bulk heterojunction (BHJ) solution processing strategy, which effectively provided a nanoscale phase-separated morphology, aiding in the separation of Coulombically bound excitons and facilitating charge transport and extraction. Compared with the application of the layer-by-layer (LbL) approach proposed in the same period, the BHJ spin-coating technology shows overwhelming advantages for evaluating the performance of photovoltaic materials and achieving more-efficient photoelectric conversion. Thus, in this study, we have further compared the BHJ and LbL processing strategies via the doctor-blade coating technology because it is a roll-to-roll compatible high-throughput thin film fabrication route. We systematically evaluated multiple target parameters, including morphological characteristics, optical simulation, physical kinetics, device efficiency, and blend stability issues. It is worth emphasizing that our findings disprove the old stereotypes such as the BHJ processing method is superior to the LbL technology for the preparation of high-performance OSCs and the LbL approach requires an orthogonal solvent and donor/acceptor materials with special solubility. Our studies demonstrate that the LbL blade-coating approach is a promising strategy to effectively reduce the efficiency-stability gap of OSCs and even a superior alternative to the BHJ method in commercial applications

Emergent molecular traits of lettuce and tomato grown under wavelength-selective solar cells

The integration of semi-transparent organic solar cells (ST-OSCs) in greenhouses offers new agrivoltaic opportunities to meet the growing demands for sustainable food production. The tailored absorption/transmission spectra of ST-OSCs impacts the power generated as well as crop growth, development and responses to the biotic and abiotic environments. To characterize crop responses to ST-OSCs, we grew lettuce and tomato, traditional greenhouse crops, under three ST-OSC filters that create different light spectra. Lettuce yield and early tomato development are not negatively affected by the modified light environment. Our genomic analysis reveals that lettuce production exhibits beneficial traits involving nutrient content and nitrogen utilization while select ST-OSCs impact regulation of flowering initiation in tomato. These results suggest that ST-OSCs integrated into greenhouses are not only a promising technology for energy-neutral, sustainable and climate-change protected crop production, but can deliver benefits beyond energy considerations

Semi-paracrystallinity in semi-conducting polymers

This article is part of the themed collections: 2022 Horizons Outstanding Paper Award Winners and Materials Horizons 2022 Most Popular Articles.Precise determination of structural organization of semi-conducting polymers is of paramount importance for the further development of these materials in organic electronic technologies. Yet, prior characterization of some of the best-performing materials for transistor and photovoltaic applications, which are based on polymers with rigid backbones, often resulted in conundrums in which X-ray scattering and microscopy yielded seemingly contradicting results. Here we solve the paradox by introducing a new structural model, i.e., semi-paracrystalline organization. The model establishes that the microstructure of these materials relies on a dense array of small paracrystalline domains embedded in a more disordered matrix. Thus, the overall structural order relies on two parameters: the novel concept of degree of paracrystallinity (i.e., paracrystalline volume/mass fraction, introduced here for the first time) and the lattice distortion parameter of paracrystalline domains (g-parameter from X-ray scattering). Structural parameters of the model are correlated with long-range charge carrier transport, revealing that charge transport in semi-paracrystalline materials is particularly sensitive to the interconnection of paracrystalline domains.Peer reviewe

From generation to collection – impact of deposition temperature on charge carrier dynamics of high-performance vacuum-processed organic solar cells

Vacuum-processed organic solar cells (VP-OSCs) possess many advantages for scalability. However, as the academic community focusses on high performing solution-processed OSCs, detailed studies about the relation between morphology and device characteristics in VP-OSCs are rare. Here, we present a study on a model donor/fullerene VP-OSC system deposited at different substrate temperatures. Substrate heating results in increases in current density and fill factor (FF). Changes in morphology are characterised by grazing-incidence wide-angle scattering (GIWAXS) and resonant soft X-ray scattering (RSoXS). The increase in the degree of crystallinity and preferential orientation of the donor molecule in heated samples results in enhanced absorption increasing current density. The exciton and charge separation efficiency were studied by transient absorption and photoluminescence quenching and only showed minor differences. To study the FF differences, charge transport and non-geminate recombination are studied by optoelectronic measurements and device simulations. The charge carrier kinetics are governed by a large density of trap states. While the energetic disorder and non-geminate recombination under open circuit conditions remain largely unchanged, the increased effective mobility and lower transport disorder observed in photocurrent transients explain the increased collection efficiency for heated devices. We relate this to the increased donor phase purity. Our results suggest that charge recombination and transport are governed by different aspects of disorder related to amorphous and crystalline donor phases. Quantitative comparison with high FF solution-processed OSCs reveals that the low mobility limits FF. Finally, drift-diffusion simulations give an outlook for possible performance increases through further optimisation of the deposition control

Complex Morphologies and Molecular Ordering in OPVs: Critical Parameters Determined by Soft X-Ray Scattering

Dr. Ade holds appointments at NCSU since 1992 (Assist. Professor 1992-97, Assoc. Prof. 1997-2001, Prof. since 2001). He received his Ph.D. in 1990 in Physics from SUNY at Stony Brook and had joined the NCSU faculty in 1992. H. Ade received the K. F. J. Heinrich Award of the Microbeam Analysis Society (2000), a DuPont Young Faculty Award (1994-97) and an NSF Young Investigator Award (1994-1999). He was also recognized by a Sigma Xi Award of the NCSU Sigma Xi Chapter (1995) and an R&D100 Award (1990). He has delivered more than 200 invited presentations and (co)-authored over 155 research papers. He is a Fellow of the APS and AAAS and has an h-factor of 39 and a steeply raising citation rate.Presented on Thursday September 26, 2013 from 11:00 am - 12:00 pm in the Molecular Science and Engineering Building room 1201A.Runtime: 62:57 minutes.Interface structure and the quantitative composition of morphology are known to be critical for fullerene based bulk heterojunction solar cells, yet have been very difficult to study previously due to a paucity of characterization methods. Recently developed soft X-ray microscopy and scattering tools provide new avenues and contribute substantially to indentify the number of phases present and to provide a quantitative measurement of their composition fluctuations and size distribution. This led to the realization that mixed domains are prevalent in OPVs and rather than just being detrimental can have important beneficial contributions for charge generation and charge transport. Furthermore, polarized x-ray scattering can reveal preferential orientation of the donor polymer (edge-on or face-on) relative to the fullerene aggregate interface. Such ordering has previously not been observed solar cells and is shown here to be a critical factor for high performance in a number of systems