A new non-fullerene small molecule with an acceptor-donor-acceptor (A-D-A) structure, FDNCTF, incorporating fluorenedicyclopentathiophene as core and naphthyl-fused indanone as end groups, was designed and synthesized. Compared with the previous molecule FDICTF with the phenyl-fused indanone as the end groups, the extended π-conjugation at the end group has only little impact on its molecular orbital energy levels, and thus, the open-circuit voltage (Voc) of its solar cell devices has been kept high. However, its light absorption and mobility, together with the short-current density (Jsc) and the fill factor (FF), of its devices have been all improved simultaneously. Through morphology, transient absorption, and theoretical studies, it is believed that these favorable changes are caused by (1) the appropriately enhanced molecular interaction between donor/acceptor which makes the charge separation at the interface more efficient, and (2) enhanced light absorption and more ordered packing at solid state, all due to the extended end-group conjugation of this molecule. With these, the solar cells with FDNCTF as the acceptor and a wide band gap polymer PBDB-T as the donor demonstrated a high power conversion efficiency (PCE) of 11.2% with an enhanced Jsc and a maintained high Voc, and significantly improved FF of 72.7% compared with that of the devices of FDICTF with the phenyl-fused indanone as the end groups. These results indicate that the unexplored conjugation size of the end group plays a critical role for the performance of their solar cell devices.

Three acceptor-donor-acceptor (A-D-A) small molecules DCAODTBDT, DRDTBDT and DTBDTBDT using dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene as the central building block, octyl cyanoacetate, 3-octylrhodanine and thiobarbituric acid as the end groups were designed and synthesized as donor materials in solution-processed photovoltaic cells (OPVs). The impacts of these different electron withdrawing end groups on the photophysical properties, energy levels, charge carrier mobility, morphologies of blend films, and their photovoltaic properties have been systematically investigated. OPVs device based on DRDTBDT gave the best power conversion efficiency (PCE) of 8.34%, which was significantly higher than that based on DCAODTBDT (4.83%) or DTBDTBDT (3.39%). These results indicate that rather dedicated and balanced consideration of absorption, energy levels, morphology, mobility, etc. for the design of small-molecule-based OPVs (SM-OPVs) and systematic investigations are highly needed to achieve high performance for SM-OPVs.

An A-D-A-type small molecule, DCF-2HT, was synthesized using fluorene as the central block and 2-(2,3-dihydro-3-oxo-1H-inden-1-ylidene)propanedinitrile as the end groups, with one hexyl-substituted thiophene as a π bridge, for use as an acceptor material in organic solar cells. Devices based on DCF-2HT and the polymer donors PBDB-T or PTB7-Th were fabricated and optimized. Power conversion efficiencies of 5.71% and 4.83% were obtained for PBDB-T: DCF-2HT- and PTB7-Th: DCF-2HT-based devices, respectively.本文合成了一个以芴为中心核, 己基取代噻吩为桥, 双氰基茚满二酮为端基的“受体-给体-受体”型小分子(DCF-2HT), 并对基于给体材料为PBDB-T/PTB7-Th, 受体为DCF-2HT的太阳能电池器件光伏性能进行了研究. 经过一系列形貌优化, 以0.5%甲基萘为添加剂, PBDB-T和PTB7-Th为给体材料的器件效率分别优化至5.71%和4.83%.

A series of new non-fullerene small molecule acceptors (NTIC, NTIC-Me, NTIC-OMe and NTIC-F) based on the acceptor–donor–acceptor (A–D–A) architecture, using hexacyclic naphthalene-(cyclopentadithiophene) as the central unit, were designed and synthesized. The non-fullerene OSC device based on PBDB-T:NTIC showed a highest PCE of 8.63%. With a relatively high-lying LUMO level of NTIC-OMe, the PBDB-T:NTIC-OMe based device obtained a comparatively high Voc of 0.965 V and a PCE of 8.61% simultaneously. The results demonstrate that the naphthalene core is a promising building block for constructing highly efficient non-fullerene acceptors and further boosting the photovoltaic performance of the devices.

Two spirobifluorene (SF)-functioned 3D nonfullerene electron acceptors—SF-OR and SF-ORCN—that use rhodanine and 2-(1,1-dicyanomethylene)rhodanine as the terminal units, respectively, were designed and synthesized. These new acceptor materials show reversible electrochemical reduction and a high optical absorption coefficient, which are critical in device operation. Electronic and structural characterizations reveal that the inclusion of cyano group on rhodanine improve the electron accepting ability at the sacrifice of structure order, since the conjugated backbone becomes less planar, which prohibits cofacial stacking. SF-OR and SF-ORCN show good photovoltaic performances when paired with a poly(3-hexylthiophene) (P3HT) donor, and the optimized devices give power conversion efficiencies of 4.66% and 4.48%, respectively. These values are higher than that of fullerene acceptor-based control devices (3.55%), which are also among the best in small molecular nonfullerene acceptor organic solar cells based on P3HT.

A simple small molecule acceptor named DICTF, with fluorene as the central block and 2-(2,3-dihydro-3-oxo-1H-inden-1-ylidene)propanedinitrile as the end-capping groups, has been designed for fullerene-free organic solar cells. The new molecule was synthesized from widely available and inexpensive commercial materials in only three steps with a high overall yield of ∼60%. Fullerene-free organic solar cells with DICTF as the acceptor material provide a high PCE of 7.93%.

A simple small molecule acceptor named DICTF, with fluorene as the central block and 2-(2,3-dihydro-3-oxo-1H-inden-1-ylidene)propanedinitrile as the end-capping groups, has been designed for fullerene-free organic solar cells. The new molecule was synthesized from widely available and inexpensive commercial materials in only three steps with a high overall yield of ∼60%. Fullerene-free organic solar cells with DICTF as the acceptor material provide a high PCE of 7.93%.