Ultrafast Dynamics Group
Frédéric Laquai's Group

Control of charge generation

Control of charge generation and recombination in ternary polymer/polymer:fullerene photovoltaic blends using amorphous and semi-crystalline copolymers as donors

Control of charge generation and recombination in ternary polymer/polymer:fullerene photovoltaic blends using amorphous and semi-crystalline copolymers as donors

Hannah Mangold, Artem A. Bakulin, Ian A. Howard, Christian Kästner, Daniel A. M. Egbe, Harald Hoppe and Frédéric Laquai

Phys. Chem. Chem. Phys., 2014,16, 20329-20337

DOI: 10.1039/C4CP01883D

Hannah Mangold, Artem A. Bakulin, Ian A. Howard, Christian Kästner, Daniel A. M. Egbe, Harald Hoppe, Frédéric Laquai
Charge Generation, Charge Recombination, Charge-Transfer States, Geminate Recombination, Non-Geminate Recombination
2014
Charge generation and recombination processes occurring in ternary photoactive copolymer:copolymer:fullerene blends consisting of different mixing ratios between entirely amorphous and semi-crystalline PPE-PPV copolymers are investigated by transient absorption pump–probe and pump–push photocurrent spectroscopy. The experiments reveal that an excess of semi-crystalline polymer facilitates exciton dissociation into free charge carriers, slows down geminate recombination, and suppresses non-geminate recombination leading to increased short-circuit currents and high fill factors. In contrast, blends utilizing solely the amorphous polymer for their donor phase suffer from a large fraction of sub-nanosecond geminate recombination of interfacially bound charge-transfer states and also from fast non-geminate recombination of free charges, resulting in a significantly reduced photovoltaic performance. However, small fractions of the amorphous polymer blended into the semi-crystalline polymer increase the open-circuit voltage and the fill factor, while keeping the charge generation and recombination parameters largely unaltered in turn leading to an optimized device performance for the ternary PPE-PPV copolymer:copolymer:fullerene blends.


Graphical abstract: Control of charge generation and recombination in ternary polymer/polymer:fullerene photovoltaic blends using amorphous and semi-crystalline copolymers as donors