Yunke Li

High-efficiency non-fullerene organic solar cells enabled by a difluorobenzothiadiazole-based donor polymer combined with a properly matched small molecule acceptor

Here we report high-performance small molecule acceptor (SMA)-based organic solar cells (OSCs) enabled by the combination of a difluorobenzothiadiazole donor polymer named PffBT4T-2DT and a SMA named SF-PDI2. It is found that SF-PDI2 matches particularly well with PffBT4T-2DT and non-fullerene OSCs with an impressive VOC of 0.98 V, and a high power conversion efficiency of 6.3% is achieved. Our study shows that PffBT4T-2DT is a promising donor material for SMA-based OSCs, and the selection of a matching SMA is also important to achieve the best OSC performance.

A Tetraphenylethylene Core‐Based 3D Structure Small Molecular Acceptor Enabling Efficient Non‐Fullerene Organic Solar Cells

A tetraphenylethylene core-based small molecular acceptor with a unique 3D molecular structure is developed. Bulk-heterojunction blend films with a small feature size (≈20 nm) are obtained, which lead to non-fullerene organic solar cells (OSCs) with 5.5% power conversion efficiency. The work provides a new molecular design approach to efficient non-fullerene OSCs based on 3D-structured small-molecule acceptors.

High-Performance Non-Fullerene Polymer Solar Cells Based on a Pair of Donor-Acceptor Materials with Complementary Absorption Properties.

A 7.3% efficiency non-fullerene polymer solar cell is realized by combining a large-bandgap polymer PffT2-FTAZ-2DT with a small-bandgap acceptor IEIC. The complementary absorption of donor polymer and small-molecule acceptor is responsible for the high-performance of the solar-cell device. This work provides important guidance to improve the performance of non-fullerene polymer solar cells.

A Vinylene-Bridged Perylenediimide-Based Polymeric Acceptor Enabling Efficient All-Polymer Solar Cells Processed under Ambient Conditions

All-polymer solar cells with 7.57% power conversion efficiency are achieved via a new perylenediimide-based polymeric acceptor. Furthermore, the device processed in ambient air without encapsulation can still reach a high power conversion efficiency (PCE) of 7.49%, which is a significant economic advantage from an industrial processing perspective. These results represent the highest PCE achieved from perylenediimide-based polymers.

A Difluorobenzoxadiazole Building Block for Efficient Polymer Solar Cells

A difluorobenzoxadiazole building block is synthesized and utilized to construct a conjugated polymer leading to high-performance thick-film polymer solar cells with a V(OC) of 0.88 V and a power conversion efficiency of 9.4%. This new building block can be used in many possible polymer structures for various organic electro-nic applications.

Improved Performance of All-Polymer Solar Cells Enabled by Naphthodiperylenetetraimide-Based Polymer Acceptor

A new polymer acceptor, naphthodiperylenetetraimide-vinylene (NDP-V), featuring a backbone of altenating naphthodiperylenetetraimide and vinylene units is designed and applied in all-polymer solar cells (all-PSCs). With this polymer acceptor, a new record power-conversion efficiencies (PCE) of 8.59% has been achieved for all-PSCs. The design principle of NDP-V is to reduce the conformational disorder in the backbone of a previously developed high-performance acceptor, PDI-V, a perylenediimide-vinylene polymer. The chemical modifications result in favorable changes to the molecular packing behaviors of the acceptor and improved morphology of the donor-acceptor (PTB7-Th:NDP-V) blend, which is evidenced by the enhanced hole and electron transport abilities of the active layer. Moreover, the stronger absorption of NDP-V in the shorter-wavelength range offers a better complement to the donor. All these factors contribute to a short-circuit current density (J sc ) of 17.07 mA cm-2 . With a fill factor (FF) of 0.67, an average PCE of 8.48% is obtained, representing the highest value thus far reported for all-PSCs.

Efficient non-fullerene polymer solar cells enabled by tetrahedron-shaped core based 3D-structure small-molecular electron acceptors

Here we report a series of tetraphenyl carbon-group (tetraphenylmethane (TPC), tetraphenylsilane (TPSi) and tetraphenylgermane (TPGe)) core based 3D-structure non-fullerene electron acceptors, enabling efficient polymer solar cells with a power conversion efficiency (PCE) of up to ∼4.3%. The results show that TPC and TPSi core-based polymer solar cells (PSCs) perform significantly better than that based on TPGe. Our study provides a new approach for designing small molecular acceptor materials for polymer solar cells.

The influence of spacer units on molecular properties and solar cell performance of non-fullerene acceptors

Rational design of molecular acceptors for non-fullerene organic solar cells remains challenging. Here we show that the introduction of two simple methyl groups on a bithiophene-bridged perylene diimide dimer leads to two molecular acceptors with distinctly different properties and solar cell performance. This work contributes towards understanding the structure–performance relationship of high-performance molecular acceptors.

All-polymer Solar Cells with Perylenediimide Polymer Acceptors

Four polymers based on perylenediimide co-polymerized with thiophene, bithiophene, selenophone and thieno[3,2-b]thiophene were investigated as the acceptor materials in all-polymer solar cells. Two different donor polymers, poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene)-2-carboxylate-2,6-diyl] (PTB7-Th) and poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-dodecyltetradecyl)-2,2′;5′,2″;5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2DT), with suitably complementary absorption spectra and energy levels were applied and examined. Among all different donor-acceptor pairs studied here, the combination of PTB7-Th:poly[N,N′-bis(1-hexylheptyl)-3,4,9,10-perylenediimide-1,6/1,7-diyl-alt-2,5-thiophene] (PDI-Th) exhibited the best power conversion efficiency (PCE) of 5.13%, with open-circuit voltage (Voc) = 0.79 V, short-circuit current density (Jsc = 12.35 mA·cm−2 and fill-factor (FF) = 0.52. The polymer of PDI-Th acceptor used here had a regio-irregular backbone, conveniently prepared from a mixture of 1,6- and 1,7-dibromo-PDI. It is also noteworthy that neither additive nor post-treatment is required for obtaining such a cell performance.

Side-chain engineering of perylenediimide-vinylene polymer acceptors for high-performance all-polymer solar cells

The side-chain structures of conjugated molecules are well recognized to sensitively influence the crystallinity, morphology and thus carrier transport properties of organic semiconductors. Here, by varying the alkyl side-chain length in the polymer acceptors, the effect of side-chain engineering on the photovoltaic performance is systematically studied in all-polymer solar cells. Clear trends of first an increase and then a decrease in the Jsc and FF values are observed as the branched alkyl groups are extended from 4 to 8 carbons. Correspondingly, the maximum average PCE (ca. 7.40%) is attained with an acceptor bearing a branched side-chain length of seven carbon atoms.