Relation between charge carrier mobility and lifetime in organic photovoltaics

Chellappan Vijila, Samarendra P Singh, Evan Williams, Prashant Sonar, Almantas Pivrikas, Bronson Philippa, Ronald White, Elumalai Naveen Kumar, S Gomathy Sandhya, Sergey Gorelik

Research output: Contribution to journalArticlepeer-review


The relationship between charge carrier lifetime and mobility in a bulk heterojunction based organic solar cell, utilizing diketopyrrolopyrole-naphthalene co-polymer and PC71BM in the photoactive blend layer, is investigated using the photoinduced charge extraction by linearly increasing voltage technique. Light intensity, delay time, and temperature dependent experiments are used to quantify the charge carrier mobility and density as well as the temperature dependence of both. From the saturation of photoinduced current at high laser intensities, it is shown that Langevin-type bimolecular recombination is present in the studied system. The charge carrier lifetime, especially in Langevin systems, is discussed to be an ambiguous and unreliable parameter to determine the performance of organic solar cells, because of the dependence of charge carrier lifetime on charge carrier density, mobility, and type of recombination. It is revealed that the relation between charge mobility (μ) and lifetime (τ) is inversely proportional, where the μτ product is independent of temperature. The results indicate that in photovoltaic systems with Langevin type bimolecular recombination, the strategies to increase the charge lifetime might not be beneficial because of an accompanying reduction in charge carrier mobility. Instead, the focus on non-Langevin mechanisms of recombination is crucial, because this allows an increase in the charge extraction rate by improving the carrier lifetime, density, and mobility simultaneously.
Original languageEnglish
Article number184503
JournalJournal of Applied Physics
Issue number18
Publication statusPublished - 2013
Externally publishedYes


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