NDLI: Origin of gap states in the electron transport layer of organic solar cells

Content Provider	Royal Society of Chemistry (RSC)
Author	Jung, Gwan Ho Lee, Jong-Lam
Copyright Year	2013
Abstract	The mechanism of the formation of gap states in bathocuproine (BCP) used as an electron transport layer (ETL) in poly(3-hexylthiophene) and the fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) based solar cell is investigated. The photo-generated electrons in the active layer are extracted to a cathode electrode through the gap states of BCP located near the lowest unoccupied molecular orbital (LUMO) level of the electron acceptors. In the most extensively used BCP, the origin of the formation of gap states is not well understood. We show that gap states in BCP are induced by out-diffusion of P3HT molecules into the BCP layer. A Secondary Ion Mass Spectrometry (SIMS) depth profile reveals that the out-diffusion of P3HT occurs during the deposition of BCP on the P3HT:PCBM active layer. The mixing of P3HT molecules with the BCP layer induces a chemical reaction between BCP and P3HT to produce the N–S bonds (between the nitrogen from BCP and the sulfur from P3HT), which acts as gap states in BCP. The power conversion efficiency increased from 0.03% to 3.0% as the deposition rate is reduced from 5.0 Å s−1 to 0.1 Å s−1. This increase originates from the change in the diffusion length of P3HT with the deposition rate of BCP, leading to an increase in conductivity as well as the alignment of the Fermi level through the gap states.
Starting Page	3034
Ending Page	3039
Page Count	6
File Format	HTM / HTML PDF
ISSN	20507488
Volume Number	1
Issue Number	9
Journal	Journal of Materials Chemistry A
DOI	10.1039/c2ta01061e
Language	English
Publisher	Royal Society of Chemistry
Access Restriction	Open
Subject Keyword	BCP SIMS Expected shortfall Polythiophene Fullerene chemistry Carboxylic acid Ester Phenyl-C61-butyric acid methyl ester Solar cell Cathode Electrode Molecular orbital Chemical reaction Nitrogen Sulfur Diffusion Fermi level
Content Type	Text
Resource Type	Article
Subject	Chemistry Renewable Energy, Sustainability and the Environment Materials Science

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