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Post‐Deposition Activation of Latent Hydrogen‐Bonding: A New Paradigm for Enhancing the Performances of Bulk Heterojunction Solar Cells
Author(s) -
Bruni Francesco,
Sassi Mauro,
Campione Marcello,
Giovanella Umberto,
Ruffo Riccardo,
Luzzati Silvia,
Meinardi Francesco,
Beverina Luca,
Brovelli Sergio
Publication year - 2014
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201400896
Subject(s) - materials science , polymer solar cell , heterojunction , acceptor , organic solar cell , phase (matter) , polymer , nanotechnology , molecule , chemical engineering , hydrogen bond , nanoscopic scale , chemical physics , solar cell , optoelectronics , organic chemistry , chemistry , physics , engineering , composite material , condensed matter physics
Small conjugated molecules (SM) are gaining momentum as an alternative to semiconducting polymers for the production of solution‐processed bulk heterojunction (BHJ) solar cells. The major issue with SM‐BHJs is the low carrier mobility due to the scarce control on the phase‐segregation process and consequent lack of preferential percolative pathways for electrons and holes to the extraction electrodes. Here, a new paradigm for fine tuning the phase‐segregation in SM‐BHJs, based on the post‐deposition exploitation of latent hydrogen bonding in binary mixtures of PCBM with suitably functionalized electron donor molecules, is demonstrated. The strategy consist in the chemical protection of the H‐bond forming sites of the donor species with a thermo‐labile functionality whose controlled thermal cleavage leads to the formation of stable, crystalline, phase‐separated molecular aggregates. This approach allows the fine tuning of the nanoscale film connectivity and thereby to simultaneously optimize the generation of geminate carriers at the donor–acceptor interfaces and the extraction of free charges via ordered phase‐separated domains. As a result, the PV efficiency undergoes an over twenty‐fold increase with respect to control devices. This strategy, demonstrated here with mixtures of diketopyrrolopyrrole derivatives with PCBM can be extended to other molecular systems for achieving highly efficient SM‐BHJ solar cells.