| 1. |
- Lin, Yuanbao, et al.
(author)
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One-Step Blade-Coated Highly Efficient Nonfullerene Organic Solar Cells with a Self-Assembled Interfacial Layer Enabled by Solvent Vapor Annealing
- 2019
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In: Solar RRL. - : Wiley. - 2367-198X. ; 3:8
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Journal article (peer-reviewed)abstract
- A pronounced enhancement of the power conversion efficiency (PCE) by 38% is achieved in one-step doctor-blade printing organic solar cells (OSCs) via a simple solvent vapor annealing (SVA) step. The organic blend composed of a donor polymer, a nonfullerene acceptor, and an interfacial layer (IL) molecular component is found to phase-separate vertically when exposed to a solvent vapor-saturated atmosphere. Remarkably, the spontaneous formation of a fine, self-organized IL between the bulk heterojunction (BHJ) layer and the indium tin oxide (ITO) electrode facilitated by SVA yields solar cells with a significantly higher PCE (11.14%) than in control devices (8.05%) without SVA and in devices (10.06%) made with the more complex two-step doctor-blade printing method. The stratified nature of the ITO/IL/BHJ/cathode is corroborated by a range of complementary characterization techniques including surface energy, cross-sectional scanning electron microscopy, grazing incidence wide angle X-ray scattering, and X-ray photoelectron spectroscopy. This study demonstrates that a spontaneously formed IL with SVA treatment combines simplicity and precision with high device performance, thus making it attractive for large-area manufacturing of next-generation OSCs.
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| 2. |
- Xia, Yuxin, 1986-
(author)
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Polymer/polymer blends in organic photovoltaic and photodiode devices
- 2018
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Doctoral thesis (other academic/artistic)abstract
- Organic photovoltaics devices (OPV) have attracted attentions of scientist for their potential as inexpensive, lightweight, flexible and suitable for roll-to-roll production. In recent years, considerable attention has been focused on new acceptor materials, either polymeric or small molecules, to replace the once dominating fullerene derivatives. The emergence of numerous new non-fullerene materials has driven power conversion efficiency (PCE) up to 17%, attracting more and more interests of commercialization.Polymer acceptors with more morphology stability, more absorption and more desired energy levels has been intensively studied and show great potential for large area and low-cost production in the future. OPV at this moment is not yet competitive with inorganic solar cells in PCE but is more attractive in flexibility, low weight and semitransparency. In this thesis, some basic knowledges of OPV is introduced in the first few chapters, while the next chapters are focusing on polymer-polymer blends and investigating novel structures and techniques for large scale production of solar cells and photodetectors aiming at maximizing these advantages to compete with inorganic counterpart.Thermal annealing effects on polymer-polymer solar cells based is studied. Annealed devices show doubled power conversion efficiency compared to non-annealed devices. Based on the morphology—mobility examination, we conclude that the better charge transport is achieved by higher order and better interconnected networks of the bulk heterojunction in the annealed active layers. The annealing improves charge transport and extends the conjugation length of the polymers, which do help charge generation and meanwhile reduce recombination. The blend of an amorphous polymer and a semi-crystalline polymer can thus be modified by thermal annealing to double the power conversion efficiency.A novel concept of all-polymer organic photovoltaics device is demonstrated in this thesis where all the layers are made out of polymers. We use PEDOT:PSS as semitransparent anode and polyethyleneimine modified PEDOT:PSS as semitransparent cathode, both of which are slot-die printed on polyethylene terephthalate(PET). Active layers are deposited on cathode and anode surfaces by spin coating separately. These layers are then joined through a roll-to-roll compatible lamination process. This forms a semitransparent and flexible solar cell. By laminating a thin layer acceptor polymer to a thick polymer-polymer blend, we can further improve the performance by reducing traps comparing to laminating blend to blend.Flexible and semitransparent all-polymer photodiodes with different geometries can be fabricated through lamination. By choosing high band gap polymers and appropriate combination of two or more polymers, organic photodiode with low noise and high specific detectivity can be obtained. Comparison between bilayer and bulk heterojunction devices gives better understanding of the origin of noise and provides ways to improve the performance of photodiodes as detector.Noise level is a critical parameter for photodetectors. The difficulties of measuring the noise of photodetectors make some researchers prefer the estimated shot noise as the dominating one and ignore the thermal noise and 1/f noise. The latter two terms are sometimes several orders higher than the former, noting the importance of experimentally measuring noise.The use of semi-transparent photovoltaic devices causes an inevitable loss of photocurrent, as light transmitted has not been absorbed. This trivial effect also leads to a loss of photovoltage, an effect partially due to the lower photocurrent but also due to the geometry of the semitransparent photovoltaic device. We here demonstrate and evaluate this photovoltage loss in semi-transparent organic photovoltaic devices, compared with non-transparent solar cells of the same material. Semi-transparent solar cells in addition introduce photovoltage loss when formed by lamination. We document and analyze these effects for a number of polymer blends in the form of bulk heterojunctions.
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| 3. |
- Yao, Nannan, et al.
(author)
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In Situ Study the Dynamics of Blade-Coated All-Polymer Bulk Heterojunction Formation and Impact on Photovoltaic Performance of Solar Cells
- 2023
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In: Solar RRL. - : John Wiley & Sons. - 2367-198X. ; , s. 1-8
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Journal article (peer-reviewed)abstract
- All-polymer solar cells (all-PSCs) have achieved impressive progress by employing acceptors polymerized from well performing small-molecule non-fullerene acceptors. Herein, the device performance and morphology evolution in blade-coated all-PSCs based on PBDBT:PF5–Y5 blends prepared from two different solvents, chlorobenzene (CB), and ortho-xylene (o-XY) are studied. The absorption spectra in CB solution indicate more ordered conformation for PF5–Y5. The drying process of PBDBT:PF5–Y5 blends is monitored by in situ multifunctional spectroscopy and the final film morphology is characterized with ex situ techniques. Finer-mixed donor/acceptor nanostructures are obtained in CB-cast film than that in o-XY-cast ones, corresponding to more efficient charge generation in the solar cells. More importantly, the conformation of polymers in solution determines the overall film morphology and the device performance. The relatively more ordered structure in CB-cast films is beneficial for charge transport and reduced non-radiative energy loss. Therefore, to achieve high-performance all-PSCs with small energy loss, it is crucial to gain favorable aggregation in the initial stage in solution.
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| 4. |
- Yao, Nannan, 1992-, et al.
(author)
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Solution-Processed Highly Efficient Semitransparent Organic Solar Cells with Low Donor Contents
- 2021
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In: ACS Applied Energy Materials. - : American Chemical Society. - 2574-0962. ; 4:12, s. 14335-14341
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Journal article (peer-reviewed)abstract
- Semitransparent organic solar cells (ST-OSCs) are promising candidates for applications in building-integrated photovoltaics (BIPV) as windows and facades. The challenge to achieve highly efficient ST-OSCs is the trade-off between power conversion efficiency (PCE) and average visible transmittance (AVT). Herein, solution-processed ST-OSCs are demonstrated on the basis a polymer donor, PM6, and a small molecule acceptor, Y6; lowering the visible-absorbing PM6 contents in blends could increase AVT and maintain PCE. Additionally, conductive polymer PEDOT:PSS is used as the top electrode due to its high transparency, good conductivity, and solution processability. Efficient ST-OSCs with 20 wt % PM6 achieve high PCE of 7.46% and AVT of 36.4%. The light utilization efficiency (LUE) of 2.72% is among the best reported values for solution-processed ST-OSCs. This work provides a straightforward approach for solution-processed ST-OSCs by combining a low fraction of visible-wavelength-selective polymer donors with near-infrared nonfullerene acceptors to achieve high PCE and AVT simultaneously.
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