Premium
Transient Photocurrent Elucidating Carrier Dynamics and Potential of Bulk Heterojunction Solar Cells Fabricated by Thermal Precursor Approach
Author(s) -
Kudo Naoki,
Uchida Ken,
Ikoma Tadaaki,
Takahashi Kohtaro,
Kuzuhara Daiki,
Suzuki Mitsuharu,
Yamada Hiroko,
Kumagai Daichi,
Yamaguchi Yuji,
Nakayama KenIchi
Publication year - 2018
Publication title -
solar rrl
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.544
H-Index - 37
ISSN - 2367-198X
DOI - 10.1002/solr.201700234
Subject(s) - photocurrent , polymer solar cell , recombination , solar cell , charge carrier , organic solar cell , electron mobility , chemistry , materials science , heterojunction , energy conversion efficiency , alkyl , optoelectronics , analytical chemistry (journal) , organic chemistry , polymer , biochemistry , gene
Transient photocurrents are measured to clarify carrier dynamics in a series of bulk heterojunction solar cells that are composed of [6,6]‐phenyl‐C 61 ‐butyric acid methyl ester (PCBM) and diketopyrrolopyrrole‐tetrabenzoporphyrin conjugates substituted by straight alkyl groups (Cn‐DPP‐BP), of which the device parameters are largely dependent on the length of the substituted alkyl groups (Cn). The time profile of the observed transients indicates the presence of both unimolecular and bimolecular charge recombination processes in the active layer of the cells. Analysis of the photocurrent decays detected at various bias voltages using a drift model that considers charge extraction by electrodes and charge recombination in the active layer enables elucidation of the charge drift mobility, the initial photocarrier density, and the charge recombination rate constants. The bimolecular recombination rate constant is correlated with Cn and this is the main factor that determines the power conversion efficiency ( η ) of the Cn‐DPP‐BP:PCBM solar cells. The Cn‐dependent fill factor can be interpreted in terms of the bias voltage dependence of the ratio between the extraction and recombination charges ( Q ex / Q re ). Comparison of η and Q ex / Q re at the short‐circuit condition predicts that η for the Cn‐DPP‐BP:PCBM solar cell can be potentially improved up to 6%.