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Favorable Mixing Thermodynamics in Ternary Polymer Blends for Realizing High Efficiency Plastic Solar Cells
Author(s) -
Gasparini Nicola,
Kahmann Simon,
Salvador Michael,
Perea Jose Dario,
Sperlich Andreas,
Baumann Andreas,
Li Ning,
Rechberger Stefanie,
Spiecker Erdmann,
Dyakonov Vladimir,
Portale Giuseppe,
Loi Maria A.,
Brabec Christoph J.,
Ameri Tayebeh
Publication year - 2019
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.201803394
Subject(s) - ternary operation , materials science , energy conversion efficiency , organic solar cell , fullerene , polymer , polymer solar cell , acceptor , intermolecular force , polymer blend , electron acceptor , chemical physics , ternary numeral system , thermodynamics , chemical engineering , molecule , photochemistry , organic chemistry , optoelectronics , composite material , chemistry , copolymer , physics , programming language , computer science , engineering , condensed matter physics
Ternary blends with broad spectral absorption have the potential to increase charge generation in organic solar cells but feature additional complexity due to limited intermixing and electronic mismatch. Here, a model system comprising the polymers poly[5,5‐bis(2‐butyloctyl)‐(2,2‐bithiophene)‐4,4‐dicarboxylate‐alt‐5,5‐2,2‐bithiophene] (PDCBT) and PTB7‐Th and PC 70 BM as an electron accepting unit is presented. The power conversion efficiency (PCE) of the ternary system clearly surpasses the performance of either of the binary systems. The photophysics is governed by a fast energy transfer process from PDCBT to PTB7‐Th, followed by electron transfer at the PTB7‐Th:fullerene interface. The morphological motif in the ternary blend is characterized by polymer fibers. Based on a combination of photophysical analysis, GIWAXS measurements and calculation of the intermolecular parameter, the latter indicating a very favorable molecular affinity between PDCBT and PTB7‐Th, it is proposed that an efficient charge generation mechanism is possible because PTB7‐Th predominantly orients around PDCBT filaments, allowing energy to be effectively relayed from PDCBT to PTB7‐Th. Fullerene can be replaced by a nonfullerene acceptor without sacrifices in charge generation, achieving a PCE above 11%. These results support the idea that thermodynamic mixing and energetics of the polymer–polymer interface are critical design parameter for realizing highly efficient ternary solar cells with variable electron acceptors.