Jianqi Zhang

All‐Polymer Solar Cells Based on Absorption‐Complementary Polymer Donor and Acceptor with High Power Conversion Efficiency of 8.27%

High-efficiency all-polymer solar cells with less thickness-dependent behavior are demonstrated by using a low bandgap n-type conjugated polymer N2200 as acceptor and an absorption-complementary difluorobenzotriazole-based medium-bandgap polymer J51 as donor.

Conjugated Polymer–Small Molecule Alloy Leads to High Efficient Ternary Organic Solar Cells

Ternary organic solar cells are promising candidates for bulk heterojunction solar cells; however, improving the power conversion efficiency (PCE) is quite challenging because the ternary system is complicated on phase separation behavior. In this study, a ternary organic solar cell (OSC) with two donors, including one polymer (PTB7-Th), one small molecule (p-DTS(FBTTH2)2), and one acceptor (PC71BM), is fabricated. We propose the two donors in the ternary blend forms an alloy. A notable averaged PCE of 10.5% for ternary OSC is obtained due to the improvement of the fill factor (FF) and the short-circuit current density (J(sc)), and the open-circuit voltage (V(oc)) does not pin to the smaller V(oc) of the corresponding binary blends. A highly ordered face-on orientation of polymer molecules is obtained due to the formation of an alloy structure, which facilitates the enhancement of charge separation and transport and the reduction of charge recombination. This work indicates that a high crystallinity and the face-on orientation of polymers could be obtained by forming alloy with two miscible donors, thus paving a way to largely enhance the PCE of OSCs by using the ternary blend strategy.

Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells.

Solution-processable small molecules for organic solar cells have attracted intense attention for their advantages of definite molecular structures compared with their polymer counterparts. However, the device efficiencies based on small molecules are still lower than those of polymers, especially for inverted devices, the highest efficiency of which is <9%. Here we report three novel solution-processable small molecules, which contain π-bridges with gradient-decreased electron density and end acceptors substituted with various fluorine atoms (0F, 1F and 2F, respectively). Fluorination leads to an optimal active layer morphology, including an enhanced domain purity, the formation of hierarchical domain size and a directional vertical phase gradation. The optimal morphology balances charge separation and transfer, and facilitates charge collection. As a consequence, fluorinated molecules exhibit excellent inverted device performance, and an average power conversion efficiency of 11.08% is achieved for a two-fluorine atom substituted molecule.

Synergistic Effect of Polymer and Small Molecules for High‐Performance Ternary Organic Solar Cells

A ternary blend system with two donors and one acceptor provides an effective route to improve the performance of organic solar cells. A synergistic effect of polymer and small molecules is observed in ternary solar cells, and the power conversion efficiency (PCE) of the ternary system (8.40%) is higher than those of binary systems based on small molecules (7.48%) or polymers (6.85%).

Over 11% Efficiency in Tandem Polymer Solar Cells Featured by a Low‐Band‐Gap Polymer with Fine‐Tuned Properties

Highly efficient polymer solar cells with tandem structure are fabricated by using two excellent photovoltaic polymers and a highly transparent intermediate recombination layer. Power conversion efficiencies over 11% can be realized featured by a low-band-gap polymer with fine-tuned properties.

An Electron Acceptor with Porphyrin and Perylene Bisimides for Efficient Non‐Fullerene Solar Cells

A star-shaped electron acceptor based on porphyrin as a core and perylene bisimide as end groups was constructed for application in non-fullerene organic solar cells. The new conjugated molecule exhibits aligned energy levels, good electron mobility, and complementary absorption with a donor polymer. These advantages facilitate a high power conversion efficiency of 7.4 % in non-fullerene solar cells, which represents the highest photovoltaic performance based on porphyrin derivatives as the acceptor.

New Wide Band Gap Donor for Efficient Fullerene-Free All-Small-Molecule Organic Solar Cells

A new organic small molecule, DRTB-T, that incorporates a two-dimensional trialkylthienyl-substituted benzodithiophene core building block was designed and synthesized. DRTB-T has a band gap (Egopt) of 2.0 eV with a low-lying highest occupied molecular orbital (HOMO) level of -5.51 eV. Nonfullerene small-molecule solar cells consisting of DRTB-T and a nonfullerene acceptor (IC-C6IDT-IC) were constructed, and the morphology of the active layer was fine-tuned by solvent vapor annealing (SVA). The device showed a record 9.08% power conversion efficiency (PCE) with a high open-circuit voltage (Voc = 0.98 V). This is the highest PCE for a nonfullerene small-molecule organic solar cell (NFSM-OSC) reported to date. Our notable results demonstrate that the molecular design of a wide band gap (WBG) donor to create a well-matched donor-acceptor pair with a low band gap (LBG) nonfullerene small-molecule acceptor, as well as subtle morphological control, provides great potential to realize high-performance NFSM-OSCs.

Asymmetric Diketopyrrolopyrrole Conjugated Polymers for Field-Effect Transistors and Polymer Solar Cells Processed from a Nonchlorinated Solvent.

Newly designed asymmetric diketopyrrolopyrrole conjugated polymers with two different aromatic substituents possess a hole mobility of 12.5 cm(2) V(-1) s(-1) in field-effect transistors and a power conversion efficiency of 6.5% in polymer solar cells, when solution processed from a nonchlorinated toluene/diphenyl ether mixed solvent.

PBDT-TSR: a highly efficient conjugated polymer for polymer solar cells with a regioregular structure

In this study, a regioregular copolymer (PBDT-TSR) based on alkythio-substituted two dimensional conjugated benzodithiophene (2D-BDT) and asymmetric thienothiophene (TT) was synthesized through two steps. Compared with its random counterpart PBDT-TS1, the PBDT-TSR shows improved absorption properties and enhanced inter-chain π–π packing effects. The hole mobility of PBDT-TSR is higher than that of PBDT-TS1. Whats more, the enhancement of regioregularity does not have great influence on its molecular energy levels of the polymer and its miscibility with the acceptor material, PC71BM. The polymer solar cell (PSC) device fabricated by using PBDT-TSR shows a high power conversion efficiency of 10.2% with a short-circuit current density (JSC) of 17.99 mA cm−2, while the PBDT-TS1 shows a PCE of 9.74%. Overall, these results suggest that it is of great importance to investigate the influence of backbone configuration on photovoltaic performance for high efficiency conjugated polymers based on asymmetric conjugated building blocks, and to improve the regioregularity of this type of polymer should be a feasible approach to enhance their photovoltaic properties.

Oligomeric Donor Material for High‐Efficiency Organic Solar Cells: Breaking Down a Polymer

Dr. L. Yuan, Dr. J. Zhang, Dr. Y. Zhang, Dr. L. Zhu, Dr. K. Lu, Prof. Z. Wei National Center for Nanoscience and Technology Beijing 100190 , China E-mail: lvk@nanoctr.cn; weizx@nanoctr.cn Dr. L. Yuan, Prof. Z. Wei University of Chinese Academy of Sciences Beijing 100049 , China Dr. Y. Zhao, Prof. W. Yan Department of Environmental Science and Engineering Xi’an Jiaotong University Xi’an 710049 , China