Date/Time: 04-04-2018 - Wednesday - 05:00 PM - 07:00 PM
Armantas Melianas1 Vytenis Pranculis2 Donato Spoltore3 Johannes Benduhn3 Olle Inganäs4 Vidmantas Gulbinas2 Koen Vandewal3 Martijn Kemerink4

1, Stanford University, Stanford, California, United States
2, Center for Physical Sciences and Technology, Vilnius, , Lithuania
3, Institut für Angewandte Photophysik, Dresden, , Germany
4, Linkoping University, Linkoping, , Sweden

In organic solar cells continuous donor and acceptor networks are considered necessary for charge extraction, whereas discontinuous neat phases and the mixed donor-acceptor phase are generally regarded as detrimental. Here, we show experimental evidence that a continuous donor network is not strictly necessary – hole motion between isolated donor sites can occur efficiently by long-range tunneling.

Using Time-Resolved Electric-Field-Induced Second Harmonic generation (TREFISH) combined with photocurrent measurements we have measured the motion of photo-generated charges from first hopping events (with sub-picosecond time resolution) to full extraction in complete solar cell devices based on α-sexithiophene (α-6T) dispersed in a buckminsterfullerene (C60) matrix. Using vacuum deposition, we carefully vary the molar fraction of α-6T in C60 from homogeneously diluted (<10% molar), to a point where α-6T begins to form isolated aggregates (>10-25% molar) or is strongly aggregated (50% molar). We thus vary the distance between the donor sites in a controlled manner. We quantitatively show that even highly diluted α-6T sites (5.7-10% molar) in a C60 matrix enable hole transport, which occurs between isolated donor sites by hole tunneling through several C60 molecules (tunneling distance ≈ 4 nm). Furthermore, at such low donor amounts (<10% molar) electron transport in the buckminsterfullerene phase remains unperturbed, thus facilitating ambipolar transport.

These results question the relevance of ‘pristine phases’ and whether a continuous interpenetrating donor-acceptor network is the ideal morphology for charge transport. The limits of this charge transport mechanism are yet to be explored.

Meeting Program

5:00 PM–7:00 PM Apr 4, 2018 (America - Denver)

PCC North, 300 Level, Exhibit Hall C-E