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Intra‐Molecular Donor–Acceptor Interaction Effects on Charge Dissociation, Charge Transport, and Charge Collection in Bulk‐Heterojunction Organic Solar Cells
Author(s) -
Zang Huidong,
Liang Yongye,
Yu Luping,
Hu Bin
Publication year - 2011
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.201100304
Subject(s) - materials science , photocurrent , acceptor , organic solar cell , polymer solar cell , heterojunction , dissociation (chemistry) , doping , chemical physics , optoelectronics , photochemistry , solar cell , chemistry , polymer , physics , condensed matter physics , composite material
Abstract This article reports experimental studies on internal charge dissociation, transport, and collection by using magnetic field effects of photocurrent (MFE PC ) and light‐assisted dielectric response (LADR) in highly‐efficient organic solar cells based on photovoltaic polymer PTB2 and PTB4 with intra‐molecular “donor–acceptor” interaction. The MFE PC at low‐field (< 150 mT ) indicates that intra‐molecular “donor‐acceptor” interaction generates charge dissociation in un‐doped PTB2 and PTB4 films, which is similar to that in lightly doped P3HT (Poly(3‐hexylthiophene)) with 5 wt% PCBM (1‐(3‐methyloxycarbonyl)‐propyl‐1‐phenyl (6,6) C 61 ). After PTB2 and PTB4 are mixed with PCBM to form bulk‐heterojunctions, the MFE PC at high‐field (> 150 mT ) reveals that the charge‐transfer complexes formed at PTB2:PCBM and PTB4:PCBM interfaces have much lower binding energies due to stronger electron‐withdrawing abilities, as compared to the P3HT:PCBM device, towards the generation of photocurrent. Furthermore, the light‐assisted dielectric response: LADR indicates that the PTB2:PCBM and PTB4:PCBM solar cells exhibit larger capacitances relative to P3HT:PCBM device under photoexcitation. This reflects that the PTB2:PCBM and PTB4:PCBM bulk heterojunctions have more effective charge transport and collection than the P3HT:PCBM counterpart. As a result, our experimental results indicate that intra‐molecular “donor‐acceptor” interaction plays an important role to enhance charge dissociation, transport, and collection in bulk‐heterojunction organic solar cells.