Fuwen Zhao

High-Performance Electron Acceptor with Thienyl Side Chains for Organic Photovoltaics

We develop an efficient fused-ring electron acceptor (ITIC-Th) based on indacenodithieno[3,2-b]thiophene core and thienyl side-chains for organic solar cells (OSCs). Relative to its counterpart with phenyl side-chains (ITIC), ITIC-Th shows lower energy levels (ITIC-Th: HOMO = -5.66 eV, LUMO = -3.93 eV; ITIC: HOMO = -5.48 eV, LUMO = -3.83 eV) due to the σ-inductive effect of thienyl side-chains, which can match with high-performance narrow-band-gap polymer donors and wide-band-gap polymer donors. ITIC-Th has higher electron mobility (6.1 × 10(-4) cm(2) V(-1) s(-1)) than ITIC (2.6 × 10(-4) cm(2) V(-1) s(-1)) due to enhanced intermolecular interaction induced by sulfur-sulfur interaction. We fabricate OSCs by blending ITIC-Th acceptor with two different low-band-gap and wide-band-gap polymer donors. In one case, a power conversion efficiency of 9.6% was observed, which rivals some of the highest efficiencies for single junction OSCs based on fullerene acceptors.

A Facile Planar Fused-Ring Electron Acceptor for As-Cast Polymer Solar Cells with 8.71% Efficiency

A planar fused-ring electron acceptor (IC-C6IDT-IC) based on indacenodithiophene is designed and synthesized. IC-C6IDT-IC shows strong absorption in 500-800 nm with extinction coefficient of up to 2.4 × 10(5) M(-1) cm(-1) and high electron mobility of 1.1 × 10(-3) cm(2) V(-1) s(-1). The as-cast polymer solar cells based on IC-C6IDT-IC without additional treatments exhibit power conversion efficiencies of up to 8.71%.

Single‐Junction Binary‐Blend Nonfullerene Polymer Solar Cells with 12.1% Efficiency

A new fluorinated nonfullerene acceptor, ITIC-Th1, has been designed and synthesized by introducing fluorine (F) atoms onto the end-capping group 1,1-dicyanomethylene-3-indanone (IC). On the one hand, incorporation of F would improve intramolecular interaction, enhance the push-pull effect between the donor unit indacenodithieno[3,2-b]thiophene and the acceptor unit IC due to electron-withdrawing effect of F, and finally adjust energy levels and reduce bandgap, which is beneficial to light harvesting and enhancing short-circuit current density (JSC ). On the other hand, incorporation of F would improve intermolecular interactions through CF···S, CF···H, and CF···π noncovalent interactions and enhance electron mobility, which is beneficial to enhancing JSC and fill factor. Indeed, the results show that fluorinated ITIC-Th1 exhibits redshifted absorption, smaller optical bandgap, and higher electron mobility than the nonfluorinated ITIC-Th. Furthermore, nonfullerene organic solar cells (OSCs) based on fluorinated ITIC-Th1 electron acceptor and a wide-bandgap polymer donor FTAZ based on benzodithiophene and benzotriazole exhibit power conversion efficiency (PCE) as high as 12.1%, significantly higher than that of nonfluorinated ITIC-Th (8.88%). The PCE of 12.1% is the highest in fullerene and nonfullerene-based single-junction binary-blend OSCs. Moreover, the OSCs based on FTAZ:ITIC-Th1 show much better efficiency and better stability than the control devices based on FTAZ:PC71 BM (PCE = 5.22%).

Mapping Polymer Donors toward High-Efficiency Fullerene Free Organic Solar Cells.

Five polymer donors with distinct chemical structures and different electronic properties are surveyed in a planar and narrow-bandgap fused-ring electron acceptor (IDIC)-based organic solar cells, which exhibit power conversion efficiencies of up to 11%.

Single crystalline indene-C60 bisadduct: isolation and application in polymer solar cells

Six fractions of indene-C60 bisadducts (IC60BAs) with two indene pendants located at different positions of the C60 cage were isolated by using the HPLC technique, in which one enantiomeric mixture was purified and the structure was confirmed by single crystal XRD analysis. It was revealed that the isolated IC60BA isomers possess an elevated LUMO energy level and afford increased electron mobility, but the solar cells assembled by the isolated IC60BA isomers with P3HT did not show high performance due to a serious phase separation between them. The results suggest that for high performance polymer solar cells we should consider not only the energy level matching between the donor and acceptor materials, but also the structural matching between them.

Heterologous production of Pseudomonas aeruginosa rhamnolipid under anaerobic conditions for microbial enhanced oil recovery

The ex situ application of rhamnolipid to enhance oil recovery is costly and complex in terms of rhamnolipid production and transportation, while in situ production of rhamnolipid is restricted by the oxygen‐deficient environments of oil reservoirs. To overcome the oxygen‐limiting conditions and to circumvent the complex regulation of rhamnolipid biosynthesis in Pseudomonas aeruginosa, an engineered strain Pseudomonas stutzeri Rhl was constructed for heterologous production of rhamnolipid under anaerobic conditions.

Matching Charge Extraction Contact for Wide-Bandgap Perovskite Solar Cells

Efficient wide-bandgap (WBG) perovskite solar cells are needed to boost the efficiency of silicon solar cells to beyond Schottky-Queisser limit, but they suffer from a larger open circuit voltage (VOC ) deficit than narrower bandgap ones. Here, it is shown that one major limitation of VOC in WBG perovskite solar cells comes from the nonmatched energy levels of charge transport layers. Indene-C60 bisadduct (ICBA) with higher-lying lowest-unoccupied-molecular-orbital is needed for WBG perovskite solar cells, while its energy-disorder needs to be minimized before a larger VOC can be observed. A simple method is applied to reduce the energy disorder by isolating isomer ICBA-tran3 from the as-synthesized ICBA-mixture. WBG perovskite solar cells with ICBA-tran3 show enhanced VOC by 60 mV, reduced VOC deficit of 0.5 V, and then a record stabilized power conversion efficiency of 18.5%. This work points out the importance of matching the charge transport layers in perovskite solar cells when the perovskites have a different composition and energy levels.

Optimization of culture medium for anaerobic production of rhamnolipid by recombinant Pseudomonas stutzeri Rhl for microbial enhanced oil recovery

Response surface methodology was employed to enhance the anaerobic production of rhamnolipid by recombinant Pseudomonas stutzeri Rhl. Glycerol is a promising carbon source used to anaerobically produce rhamnolipid. In a Plackett–Burman design, glycerol, KH2PO4 and yeast extract were significant factors. The proposed optimized medium contained the following: 46·55 g l−1 glycerol; 3 g l−1 NaNO3; 5·25 g l−1 K2HPO4·3H2O; 5·71 g l−1 KH2PO4; 0·40 g l−1 MgSO4·7H2O; 0·13 g l−1 CaCl2; 1·0 g l−1 KCl; 1·0 g l−1 NaCl; and 2·69 g l−1 yeast extract. Using this optimized medium, we obtained an anaerobic yield of rhamnolipid of 3·12 ± 0·11 g l−1 with a 0·85‐fold increase. Core flooding test results also revealed that Ps. stutzeri Rhl grown in an optimized medium enhanced the oil recovery efficiency by 15·7%, which was 6·6% higher than in the initial medium. Results suggested that the optimized medium is a promising nutrient source that could effectively mobilize oil by enhancing the in situ production of rhamnolipid.

Rhodanine flanked indacenodithiophene as non-fullerene acceptor for efficient polymer solar cells

A fused-ring electron acceptor IDT-2BR1 based on indacenodithiophene core with hexyl side-chains flanked by benzothiadiazole rhodanine was designed and synthesized. In comparison with its counterpart with hexylphenyl side-chains (IDT-2BR), IDT-2BR1 exhibits higher highest occupied molecular orbital (HOMO) energy but similar lowest unoccupied molecular orbital (LUMO) energy (IDT-2BR1: HOMO=−5.37 eV, LUMO=−3.67 eV; IDT-2BR: HOMO=−5.52 eV, LUMO=−3.69 eV), red-shifted absorption and narrower bandgap. IDT-2BR1 has higher electron mobility (2.2×10–3 cm2 V–1 s–1) than IDT-2BR (3.4×10–4 cm2 V–1 s–1) due to the reduced steric hindrance and ordered molecular packing. Fullerene-free organic solar cells based on PTB7-Th:IDT-2BR1 yield power conversion efficiencies up to 8.7%, higher than that of PTB7-Th:IDT-2BR (7.7%), with a high open circuit voltage of 0.95 V and good device stability.

Balanced Partnership between Donor and Acceptor Components in Nonfullerene Organic Solar Cells with >12% Efficiency

Relative to electron donors for bulk heterojunction organic solar cells (OSCs), electron acceptors that absorb strongly in the visible and even near-infrared region are less well developed, which hinders the further development of OSCs. Fullerenes as traditional electron acceptors have relatively weak visible absorption and limited electronic tunability, which constrains the optical and electronic properties required of the donor. Here, high-performance fullerene-free OSCs based on a combination of a medium-bandgap polymer donor (FTAZ) and a narrow-bandgap nonfullerene acceptor (IDIC), which exhibit complementary absorption, matched energy levels, and blend with pure phases on the exciton diffusion length scale, are reported. The single-junction OSCs based on the FTAZ:IDIC blend exhibit power conversion efficiencies up to 12.5% with a certified value of 12.14%. Transient absorption spectroscopy reveals that exciting either the donor or the acceptor component efficiently generates mobile charges, which do not suffer from recombination to triplet states. Balancing photocurrent generation between the donor and nonfullerene acceptor removes undesirable constraints on the donor imposed by fullerene derivatives, opening a new avenue toward even higher efficiency for OSCs.