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Enhancing Open‐Circuit Voltage in Gradient Organic Solar Cells by Rectifying Thermalization Losses
Author(s) -
Andersson Olof,
Kemerink Martijn
Publication year - 2020
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.202000400
Subject(s) - thermalisation , organic solar cell , materials science , anode , open circuit voltage , optoelectronics , non equilibrium thermodynamics , cathode , theory of solar cells , voltage , photovoltaics , photovoltaic system , heterojunction , polymer solar cell , chemical physics , computational physics , solar cell , chemistry , atomic physics , physics , electrical engineering , thermodynamics , polymer , electrode , engineering , quantum mechanics , composite material
In virtually all solar cells, including optimized ones that operate close to the Shockley–Queisser (SQ) limit, thermalization losses are a major, efficiency‐limiting factor. In typical bulk heterojunction organic solar cells, the loss of the excess energy of photocreated charge carriers in the disorder‐broadened density of states is a relatively slow process that for commonly encountered disorder values takes longer than the charge extraction time. Herein, it is demonstrated by numerical modeling that this slow relaxation can be rectified by means of a linear gradient in the donor:acceptor ratio between anode and cathode. For experimentally relevant parameters, open‐circuit voltage ( V OC ) enhancements up to ≈0.2 V in combination with significant enhancements in fill factor as compared to devices without gradient are found. TheV OCenhancement can be understood in terms of a simple nonequilibrium effective temperature model. Implications for existing and future organic photovoltaics (OPV) devices are discussed.