Tao Liu

High-Performance Solution-Processed Non-Fullerene Organic Solar Cells Based on Selenophene-Containing Perylene Bisimide Acceptor

Non-fullerene acceptors have recently attracted tremendous interest because of their potential as alternatives to fullerene derivatives in bulk heterojunction organic solar cells. However, the power conversion efficiencies (PCEs) have lagged far behind those of the polymer/fullerene system, mainly because of the low fill factor (FF) and photocurrent. Here we report a novel perylene bisimide (PBI) acceptor, SdiPBI-Se, in which selenium atoms were introduced into the perylene core. With a well-established wide-band-gap polymer (PDBT-T1) as the donor, a high efficiency of 8.4% with an unprecedented high FF of 70.2% is achieved for solution-processed non-fullerene organic solar cells. Efficient photon absorption, high and balanced charge carrier mobility, and ultrafast charge generation processes in PDBT-T1:SdiPBI-Se films account for the high photovoltaic performance. Our results suggest that non-fullerene acceptors have enormous potential to rival or even surpass the performance of their fullerene counterparts.

Single‐Junction Organic Solar Cells Based on a Novel Wide‐Bandgap Polymer with Efficiency of 9.7%

Prof. L. Huo, T. Liu, Prof. X. Sun, Y. Cai, Prof. Y. Sun Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education Beijing Key Laboratory of Bio-Inspired Energy Materials and Devices School of Chemistry and Environment Beihang University Beijing 100191 , P. R. China E-mail: sunym@buaa.edu.cn Prof. L. Huo, T. Liu, Prof. X. Sun, Y. Cai, Prof. A. J. Heeger, Prof. Y. Sun Heeger Beijing Research and Development Center International Research Institute for Multidisciplinary Science Beihang University Beijing 100191 , P. R. China

Ternary Organic Solar Cells Based on Two Compatible Nonfullerene Acceptors with Power Conversion Efficiency >10%

Two different nonfullerene acceptors and one copolymer are used to fabricate ternary organic solar cells (OSCs). The two acceptors show unique interactions that reduce crystallinity and form a homogeneous mixed phase in the blend film, leading to a high efficiency of ≈10.3%, the highest performance reported for nonfullerene ternary blends. This work provides a new approach to fabricate high-performance OSCs.

Alkyl Side-Chain Engineering in Wide-Bandgap Copolymers Leading to Power Conversion Efficiencies over 10%

A series of wide-bandgap (WBG) copolymers with different alkyl side chains are synthesized. Among them, copolymer PBT1-EH with moderatly bulky side chains on the acceptor unit shows the best photovoltaic performance with power conversion efficiency over 10%. The results suggest that the alkyl side-chain engineering is an effective strategy to further tuning the optoelectronic properties of WBG copolymers.

Organic Solar Cells Based on a 2D Benzo[1,2-b: 4,5-b ']difuran-Conjugated Polymer with High-Power Conversion Efficiency

A novel 2D benzodifuran (BDF)-based copolymer (PBDF-T1) is synthesized. Polymer solar cells fabricated with PBDF-T1 show high power conversion efficiency of 9.43% and fill factor of 77.4%, which is higher than the performance of its benzothiophene (BDT) counterpart (PBDT-T1). These results provide important progress for BDF-based copolymers and demonstrate that BDF-based copolymers can be competitive with the well-studied BDT counterparts via molecular structure design and device optimization.

Fine‐Tuning of Molecular Packing and Energy Level through Methyl Substitution Enabling Excellent Small Molecule Acceptors for Nonfullerene Polymer Solar Cells with Efficiency up to 12.54%

A novel small molecule acceptor MeIC with a methylated end-capping group is developed. Compared to unmethylated counterparts (ITCPTC), MeIC exhibits a higher lowest unoccupied molecular orbital (LUMO) level value, tighter molecular packing, better crystallites quality, and stronger absorption in the range of 520-740 nm. The MeIC-based polymer solar cells (PSCs) with J71 as donor, achieve high power conversion efficiency (PCE), up to 12.54% with a short-circuit current (JSC ) of 18.41 mA cm-2 , significantly higher than that of the device based on J71:ITCPTC (11.63% with a JSC of 17.52 mA cm-2 ). The higher JSC of the PSC based on J71:MeIC can be attributed to more balanced μh /μe , higher charge dissociation and charge collection efficiency, better molecular packing, and more proper phase separation features as indicated by grazing incident X-ray diffraction and resonant soft X-ray scattering results. It is worth mentioning that the as-cast PSCs based on MeIC also yield a high PCE of 11.26%, which is among the highest value for the as-cast nonfullerene PSCs so far. Such a small modification that leads to so significant an improvement of the photovoltaic performance is a quite exciting finding, shining a light on the molecular design of the nonfullerene acceptors.

High-Performance Non-Fullerene Organic Solar Cells Based on a Selenium-Containing Polymer Donor and a Twisted Perylene Bisimide Acceptor

A novel polymer donor (PBDTS‐Se) is designed to match with a non‐fullerene acceptor (SdiPBI‐S). The corresponding solar cells show a high efficiency of 8.22%, which result from synergetic improvements of light harvesting, charge carrier transport and collection, and morphology. The results indicate that rational design of novel donor materials is important for non‐fullerene organic solar cells.

Thienobenzene-fused perylene bisimide as a non-fullerene acceptor for organic solar cells with a high open-circuit voltage and power conversion efficiency

Perylene bisimide (PBI) based molecules have recently attracted tremendous interest as acceptors in non-fullerene organic solar cells. However, most PBI-based acceptors possess deep LUMO energy levels (−3.9 ∼ −4.0 eV) and show an open-circuit voltage (Voc) below 0.90 V, thus limiting the improvement of device efficiency. Here, we report two novel ring-fused PBI dimers, SdiPBI-BT and diPBI-BT, with thienobenzene fused to the bay region of the PBI subunits. Conventional bulk-heterojunction (BHJ) solar cells based on SdiPBI-BT show a power conversion efficiency (PCE) of 6.71% with a high Voc value of 0.95 V, a short-circuit current density (Jsc) of 10.31 mA cm−2 and a high fill factor (FF) of 68.7%. Devices based on diPBI-BT show a PCE of 5.84% with a high Voc value of 0.99 V. These results demonstrate that ring-fused PBI derivatives are promising materials for non-fullerene cells.

Non-planar perylenediimide acceptors with different geometrical linker units for efficient non-fullerene organic solar cells

Three perylenediimide (PDI) acceptors (P2O2, P2N2 and P4N4) were synthesized by functionalizing the bay positions of PDI with benzil, 2,3-diphenylquinoxaline and 2,3,7,8-tetraphenylpyrazino[2,3-g]quinoxaline as linkers, respectively. The photovoltaic properties of the three acceptor molecules have been investigated. The different PDI linker units show different physical and chemical properties of the PDIs. The three PDIs display different non-planar geometrical structures because of the different linker units, which affect the corresponding morphology of the blend films and also influence the charge mobility and fill factor (FF) of the organic solar cells (OSCs). Furthermore, the gradient energy levels of the three PDIs provide an efficient research model for the relationship of device open-circuit voltage (Voc) and energy levels. As the result, the P4N4 based non-fullerene devices show the best photovoltaic performance with a power conversion efficiency (PCE) of 5.71%, whereas the P2O2 and P2N2 based non-fullerene devices show relatively lower PCEs of 2.53% and 3.86%, respectively.

Optimized Fibril Network Morphology by Precise Side-Chain Engineering to Achieve High-Performance Bulk-Heterojunction Organic Solar Cells

A polymer fibril assembly can dictate the morphology framework, in forming a network structure, which is highly advantageous in bulk heterojunction (BHJ) organic solar cells (OSCs). A fundamental understanding of how to manipulate such a fibril assembly and its influence on the BHJ morphology and device performance is crucially important. Here, a series of donor-acceptor polymers, PBT1-O, PBT1-S, and PBT1-C, is used to systematically investigate the relationship between molecular structure, morphology, and photovoltaic performance. The subtle atom change in side chains is found to have profound effect on regulating electronic structure and self-assembly of conjugated polymers. Compared with PBT1-O and PBT1-S, PBT1-C-based OSCs show much higher photovoltaic performance with a record fill factor (FF) of 80.5%, due to the formation of optimal interpenetrating network morphology. Such a fibril network strategy is further extended to nonfullerene OSCs using a small-molecular acceptor, which shows a high efficiency of 12.7% and an FF of 78.5%. The results indicate the formation of well-defined fibrillar structure is a promising approach to achieving a favorable morphology in BHJ OSCs.