So far, one of the fundamental limitations of organic photovoltaic (OPV) device power conversion efficiencies (PCEs) has been the low voltage output caused by a molecular orbital mismatch between the donor polymer and acceptor molecules. Here, we present a means of addressing the low voltage output by introducing novel trimetallic nitride endohedral fullerenes (TNEFs) as acceptor materials for use in photovoltaic devices. TNEFs were discovered in 1999 by Stevenson et al. ; for the first time derivatives of the TNEF acceptor, Lu(3)N@C(80), are synthesized and integrated into OPV devices. The reduced energy offset of the molecular orbitals of Lu(3)N@C(80) to the donor, poly(3-hexyl)thiophene (P3HT), reduces energy losses in the charge transfer process and increases the open circuit voltage (Voc) to 260 mV above reference devices made with [6,6]-phenyl-C(61)-butyric methyl ester (C(60)-PCBM) acceptor. PCEs >4% have been observed using P3HT as the donor material. This work clears a path towards higher PCEs in OPV devices by demonstrating that high-yield charge separation can occur with OPV systems that have a reduced donor/acceptor lowest unoccupied molecular orbital energy offset.

Two isomeric [5,6]-pyrrolidine-I h -Sc 3 N@C 80 electron donor acceptor conjugates containing triphenylamine (TPA) as the donor system were synthesized. Electrochemical and photophysical studies of the novel conjugates were made and compared with those of their C 60 analogues, in order to determine i) the effect of the linkage position (N-substituted versus 2-substituted pyrrolidine) of the donor system in the formation of photoinduced charge separated states, ii) the thermal stability towards the retro-cycloaddition reaction and iii) the effect of changing C 60 for I h -Sc 3 N@C 80 as the electron acceptor. It was found that when the donor is connected to the pyrrolidine nitrogen atom, the resulting dyad produces a significantly longer lived radical pair than the corresponding 2-substituted isomer for both the C 60 and I h -Sc 3 N@C 80 dyads. In addition to that, the N-substituted TPA-I h -Sc 3 N@C 80 dyad has much better thermal stability than the 2-subtituted one. Finally, the I hSc 3 N@C 80 dyads have considerably longer lived charge separated states than their C 60 analogues, thus approving the advantage of using I h -Sc 3 N@C 80 instead of C 60 as the acceptor for the construction of fullerene based donor acceptor conjugates. These findings are important for the design and future application of I h -Sc 3 N@C 80 dyads as materials for the construction of plastic organic solar cells.

Here the influence that 1‐(3‐hexoxycarbonyl)propyl‐1‐phenyl‐[6,6]‐Lu3N@C81, Lu3N@C80–PCBH, a novel acceptor material, has on active layer morphology and the performance of organic photovoltaic (OPV) devices using this material is reported. Polymer/fullerene blend films with poly(3‐hexylthiophene), P3HT, donor material and Lu3N@C80–PCBH acceptor material are studied using absorption spectroscopy, grazing incident X‐ray diffraction and photocurrent spectra of photovoltaic devices. Due to a smaller molecular orbital offset the OPV devices built with Lu3N@C80–PCBH display increased open circuit voltage over empty cage fullerene acceptors. The photovoltaic performance of these metallo endohedral fullerene blend films is found to be highly impacted by the fullerene loading. The results indicate that the optimized blend ratio in a P3HT matrix differs from a molecular equivalent of an optimized P3HT/[6,6]‐phenyl‐C61‐butyric methyl ester, C60–PCBM, active layer, and this is related to the physical differences of the C80 fullerene. The influence that active layer annealing has on the OPV performance is further evaluated. Through properly matching the film processing and the donor/acceptor ratio, devices with power conversion efficiency greater than 4% are demonstrated.