Author
Andrew C. Stuart
Other affiliations: California Institute of Technology
Bio: Andrew C. Stuart is an academic researcher from University of North Carolina at Chapel Hill. The author has contributed to research in topics: Polymer solar cell & Organic solar cell. The author has an hindex of 12, co-authored 14 publications receiving 3927 citations. Previous affiliations of Andrew C. Stuart include California Institute of Technology.
Papers
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TL;DR: The resulting fluorinated polymer PBnDT-FTAZ outperforms poly(3-hexylthiophene), the current medium band gap polymer of choice, and thus is a viable candidate for use in highly efficient tandem cells.
Abstract: Recent research advances on conjugated polymers for photovoltaic devices have focused on creating low band gap materials, but a suitable band gap is only one of many performance criteria required for a successful conjugated polymer. This work focuses on the design of two medium band gap (∼2.0 eV) copolymers for use in photovoltaic cells which are designed to possess a high hole mobility and low highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels. The resulting fluorinated polymer PBnDT−FTAZ exhibits efficiencies above 7% when blended with [6,6]-phenyl C61-butyric acid methyl ester in a typical bulk heterojunction, and efficiencies above 6% are still maintained at an active layer thicknesses of 1 μm. PBnDT−FTAZ outperforms poly(3-hexylthiophene), the current medium band gap polymer of choice, and thus is a viable candidate for use in highly efficient tandem cells. PBnDT−FTAZ also highlights other performance criteria which contribute to high photovoltaic efficiency, bes...
1,463 citations
TL;DR: F fluorine is the mostelectronegative element, with a Pauling electronegativity of 4.0, which is much larger than that of hydrogen (2.2), and these fluorine atoms often have a great influence on inter- and intramolecular interaction.
Abstract: a) fluorine is the mostelectronegative element, with a Pauling electronegativity of4.0, which is much larger than that of hydrogen (2.2);b) fluorine is the smallest electron-withdrawing group (vander Waals radius, r=1.35 , only slightly larger than hydro-gen, r=1.2 ). Furthermore, these fluorine atoms often havea great influence on inter- and intramolecular interactionsthrough C-F···H, F···S, and C-F···p
1,183 citations
TL;DR: The disclosed "fluorine" impact not only explains the efficiency increase from 4% of PBnDT-DTBT (0F) to 7% with PBn DT-DTffBT (2F) but also suggests fluorine substitution should be generally considered in the future design of new polymers.
Abstract: Three structurally identical polymers, except for the number of fluorine substitutions (0, 1, or 2) on the repeat unit (BnDT-DTBT), are investigated in detail, to further understand the impact of these fluorine atoms on open circuit voltage (Voc), short circuit current (Jsc), and fill factor (FF) of related solar cells. While the enhanced Voc can be ascribed to a lower HOMO level of the polymer by adding more fluorine substituents, the improvement in Jsc and FF are likely due to suppressed charge recombination. While the reduced bimolecular recombination with raising fluorine concentration is confirmed by variable light intensity studies, a plausibly suppressed geminate recombination is implied by the significantly increased change of dipole moment between the ground and excited states (Δμge) for these polymers as the number of fluorine substituents increases. Moreover, the 2F polymer (PBnDT-DTffBT) exhibits significantly more scattering in the in-plane lamellar stacking and out-of-plane π–π stacking dire...
520 citations
TL;DR: X-ray scattering experiments indicate that the molecular orientation at the interfaces of bulk heterojunction organic solar cells influences the cells' fill factor and short-circuit current as discussed by the authors, which is very interesting.
Abstract: X-ray scattering experiments indicate that the molecular orientation at the interfaces of bulk heterojunction organic solar cells influences the cells’ fill factor and short-circuit current.
430 citations
TL;DR: In this article, the authors summarized four design criteria for conjugated polymer photovoltaic materials: high oxidation potential, low band gap, a planar symmetrical structure, and high molecular weight.
Abstract: This study centers upon the summarized four design criteria for conjugated polymer photovoltaic materials: high oxidation potential, low band gap, a planar symmetrical structure, and high molecular weight. Two polymer materials were synthesized to fulfill these design criteria, both based upon copolymers of benzo[1,2-b:4,5-b′]dithiophene (BnDT) and 4,7-di(2-thienyl)-2,1,3-benzothiadiazole (DTBT). Additional hexyl chains were added to one polymer on the 4 position of the DTBT unit, which increased the molecular weight of the polymer without detracting from its electrochemical or optical properties. Both polymers perform exceptionally well in preliminary bulk heterojunction solar cells, reaching power conversion efficiencies greater than 4%.
137 citations
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TL;DR: In this article, a review summarizes recent progress in the development of polymer solar cells and provides a synopsis of major achievements in the field over the past few years, while potential future developments and the applications of this technology are also briefly discussed.
Abstract: This Review summarizes recent progress in the development of polymer solar cells. It covers the scientific origins and basic properties of polymer solar cell technology, material requirements and device operation mechanisms, while also providing a synopsis of major achievements in the field over the past few years. Potential future developments and the applications of this technology are also briefly discussed.
3,832 citations
TL;DR: The uncovered aggregation and design rules yield three high-efficiency (>10%) donor polymers and will allow further synthetic advances and matching of both the polymer and fullerene materials, potentially leading to significantly improved performance and increased design flexibility.
Abstract: Although the field of polymer solar cell has seen much progress in device performance in the past few years, several limitations are holding back its further development For instance, current high-efficiency (>90%) cells are restricted to material combinations that are based on limited donor polymers and only one specific fullerene acceptor Here we report the achievement of high-performance (efficiencies up to 108%, fill factors up to 77%) thick-film polymer solar cells for multiple polymer:fullerene combinations via the formation of a near-ideal polymer:fullerene morphology that contains highly crystalline yet reasonably small polymer domains This morphology is controlled by the temperature-dependent aggregation behaviour of the donor polymers and is insensitive to the choice of fullerenes The uncovered aggregation and design rules yield three high-efficiency (>10%) donor polymers and will allow further synthetic advances and matching of both the polymer and fullerene materials, potentially leading to significantly improved performance and increased design flexibility
2,839 citations
TL;DR: The development of a high-performance low bandgap polymer that enables a solution processed tandem solar cell with certified 10.6% power conversion efficiency under standard reporting conditions, which is the first certified polymer solar cell efficiency over 10%.
Abstract: An effective way to improve polymer solar cell efficiency is to use a tandem structure, as a broader part of the spectrum of solar radiation is used and the thermalization loss of photon energy is minimized. In the past, the lack of high-performance low-bandgap polymers was the major limiting factor for achieving high-performance tandem solar cell. Here we report the development of a high-performance low bandgap polymer (bandgap 60% and spectral response that extends to 900 nm, with a power conversion efficiency of 7.9%. The polymer enables a solution processed tandem solar cell with certified 10.6% power conversion efficiency under standard reporting conditions (25 °C, 1,000 Wm(-2), IEC 60904-3 global), which is the first certified polymer solar cell efficiency over 10%.
2,708 citations
TL;DR: This Account discusses the basic requirements and scientific issues in the molecular design of high efficiency photovoltaic molecules, and summarizes recent progress in electronic energy level engineering and absorption spectral broadening of the donor and acceptor photvoltaic materials by my research group and others.
Abstract: Bulk heterojunction (BHJ) polymer solar cells (PSCs) sandwich a blend layer of conjugated polymer donor and fullerene derivative acceptor between a transparent ITO positive electrode and a low work function metal negative electrode. In comparison with traditional inorganic semiconductor solar cells, PSCs offer a simpler device structure, easier fabrication, lower cost, and lighter weight, and these structures can be fabricated into flexible devices. But currently the power conversion efficiency (PCE) of the PSCs is not sufficient for future commercialization. The polymer donors and fullerene derivative acceptors are the key photovoltaic materials that will need to be optimized for high-performance PSCs.In this Account, I discuss the basic requirements and scientific issues in the molecular design of high efficiency photovoltaic molecules. I also summarize recent progress in electronic energy level engineering and absorption spectral broadening of the donor and acceptor photovoltaic materials by my researc...
2,527 citations
TL;DR: The PBDB-T-SF:IT-4F-based OSC device showed a record high efficiency, and an efficiency of over 12% can be obtained with a thickness of 100-200 nm, suggesting the promise of fullerene-free OSCs in practical applications.
Abstract: A new polymer donor (PBDB-T-SF) and a new small molecule acceptor (IT-4F) for fullerene-free organic solar cells (OSCs) were designed and synthesized The influences of fluorination on the absorption spectra, molecular energy levels, and charge mobilities of the donor and acceptor were systematically studied The PBDB-T-SF:IT-4F-based OSC device showed a record high efficiency of 131%, and an efficiency of over 12% can be obtained with a thickness of 100–200 nm, suggesting the promise of fullerene-free OSCs in practical applications
2,292 citations