Premium
Trap‐Assisted Recombination via Integer Charge Transfer States in Organic Bulk Heterojunction Photovoltaics
Author(s) -
Bao Qinye,
Sandberg Oskar,
Dagnelund Daniel,
Sandén Simon,
Braun Slawomir,
Aarnio Harri,
Liu Xianjie,
Chen Weimin M.,
Österbacka Ronald,
Fahlman Mats
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.201401513
Subject(s) - organic solar cell , materials science , acceptor , open circuit voltage , photovoltaics , optoelectronics , electron affinity (data page) , polymer solar cell , fullerene , heterojunction , photovoltaic system , chemical physics , solar cell , voltage , condensed matter physics , physics , chemistry , electrical engineering , polymer , organic chemistry , molecule , engineering , quantum mechanics , composite material
Organic photovoltaics are under intense development and significant focus has been placed on tuning the donor ionization potential and acceptor electron affinity to optimize open circuit voltage. Here, it is shown that for a series of regioregular‐poly(3‐hexylthiophene):fullerene bulk heterojunction (BHJ) organic photovoltaic devices with pinned electrodes, integer charge transfer states present in the dark and created as a consequence of Fermi level equilibrium at BHJ have a profound effect on open circuit voltage. The integer charge transfer state formation causes vacuum level misalignment that yields a roughly constant effective donor ionization potential to acceptor electron affinity energy difference at the donor–acceptor interface, even though there is a large variation in electron affinity for the fullerene series. The large variation in open circuit voltage for the corresponding device series instead is found to be a consequence of trap‐assisted recombination via integer charge transfer states. Based on the results, novel design rules for optimizing open circuit voltage and performance of organic bulk heterojunction solar cells are proposed.