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Recombination in Polymer:Fullerene Solar Cells with Open‐Circuit Voltages Approaching and Exceeding 1.0 V
Author(s) -
Hoke Eric T.,
Vandewal Koen,
Bartelt Jonathan A.,
Mateker William R.,
Douglas Jessica D.,
Noriega Rodrigo,
Graham Kenneth R.,
Fréchet Jean M. J.,
Salleo Alberto,
McGehee Michael D.
Publication year - 2013
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201200474
Subject(s) - fullerene , materials science , photoluminescence , open circuit voltage , photocurrent , exciton , acceptor , optoelectronics , quantum efficiency , organic solar cell , band gap , polymer solar cell , polymer , solar cell , analytical chemistry (journal) , voltage , physics , chemistry , composite material , condensed matter physics , chromatography , quantum mechanics
Abstract Polymer:fullerene solar cells are demonstrated with power conversion efficiencies over 7% with blends of PBDTTPD and PC 61 BM. These devices achieve open‐circuit voltages ( V oc ) of 0.945 V and internal quantum efficiencies of 88%, making them an ideal candidate for the large bandgap junction in tandem solar cells. V oc ’s above 1.0 V are obtained when the polymer is blended with multiadduct fullerenes; however, the photocurrent and fill factor are greatly reduced. In PBDTTPD blends with multiadduct fullerene ICBA, fullerene emission is observed in the photoluminescence and electroluminescence spectra, indicating that excitons are recombining on ICBA. Voltage‐dependent, steady state and time‐resolved photoluminescence measurements indicate that energy transfer occurs from PBDTTPD to ICBA and that back hole transfer from ICBA to PBDTTPD is inefficient. By analyzing the absorption and emission spectra from fullerene and charge transfer excitons, we estimate a driving free energy of –0.14 ± 0.06 eV is required for efficient hole transfer. These results suggest that the driving force for hole transfer may be too small for efficient current generation in polymer:fullerene solar cells with V oc values above 1.0 V and that non‐fullerene acceptor materials with large optical gaps (>1.7 eV) may be required to achieve both near unity internal quantum efficiencies and values of V oc exceeding 1.0 V.