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Investigation of Driving Forces for Charge Extraction in Organic Solar Cells: Transient Photocurrent Measurements on Solar Cells Showing S‐Shaped Current–Voltage Characteristics
Author(s) -
Tress Wolfgang,
Corvers Steef,
Leo Karl,
Riede Moritz
Publication year - 2013
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.201200931
Subject(s) - photocurrent , materials science , charge carrier , diffusion , optoelectronics , voltage , diffusion current , drift current , heterojunction , extraction (chemistry) , electric field , transient (computer programming) , current (fluid) , open circuit voltage , charge (physics) , theory of solar cells , redistribution (election) , organic solar cell , photoconductivity , solar cell , polymer solar cell , electrical engineering , physics , chemistry , polymer , thermodynamics , computer science , law , composite material , operating system , chromatography , quantum mechanics , political science , politics , engineering
The role of drift and diffusion as driving forces for charge carrier extraction in flat heterojunction organic solar cells is examined at the example of devices showing intentional S‐shaped current–voltage ( J‐V ) characteristics. Since these kinks are related to energy barriers causing a redistribution of the electric field and charge carrier density gradients, they are suitable for studying the limits of charge extraction. The dynamics of this redistribution process are experimentally monitored via transient photocurrents, where the current response on square pulses of light is measured in the μs to ms regime. In combination with drift‐diffusion simulation data, we demonstrate a pile‐up of charge carriers at extraction barriers and a high contribution of diffusion to photocurrent in the case of injection barriers. Both types of barrier lead to S‐kinks in the J‐V curve and can be distinguished from each other and from other reasons for S‐kinks (e.g. imbalanced mobilities) by applying the presented approach. Furthermore, it is also helpful to investigate the driving forces for charge extraction in devices without S‐shaped J‐V curve close to open circuit to evaluate whether their electrodes are optimized.