What is the typical charge carrier lifetime(s) in organic semiconductors? I'm interested in material used in organic solar cells. How do these values compare with the values for inorganic crystalline semiconductors like Si?( Which has the higher charge carrier lifetime?)
Hi,
You can find interesting details about electron and home lifetime in Organic solar cell in the publication titled "Charge carrier lifetime and recombination in Bulk Heterojunction solar cell" by A. Pivrikas et al, IEEE Journal of Selected topics in quantum electronics, Dec. 2010.
Carrier lifetime depends upon the density of impurities and imperfections in the semiconductor. Silicon has the highest carrier lifetime because it is not only the purest material made so far, but also it is the most perfect crystal realised by technology. The electron/hole lifetime can be as high as 1 ms in the purest and most perfect silicon; high impurity density and/or lifetime killers like Au impurity can bring the lifetime down to 1 ns.
Typical carrier lifetime in organic semiconductors may be 1 microsecond.
From what I know organic carrier lifetimes are typically in the ns range. High quality inorganic semiconductors with a direct band gap, like GaAs, also have lifetimes in the low ns range, high quality indirect gap materials like Si can reach up to 10ms or so. It's worth noting that in Si this makes the diffusion length so high that surface defects can limit lifetime, rather than the bulk crystal.
Thank you for your clarifications.
So the carrier lifetime is typically less in disordered materials like organic semiconductors. What kind of techniques can be used to measure carrier lifetime? I was wondering whether the discrepancy between given ballpark values arise due to different measurement techniques employed?
Waranatha,
there are two kind of carrier lifetime measurements techniques:
- Optical measurements: such as Photoconductance Decay (PCD), Quasi-Steady-State Photoconductance (QSSPC), Short-Circuit Current/Open-Circuit Voltage Decay (SCCD/OCVD), Photoluminescence Decay (PLD), Surface Photovoltage (SPV), Steady-State Short-Circuit Current (SSSCC), Free Carrier Absorption, Electron Beam Induced Current (EBIC).
- Electrical measurements: Diode Current-Voltage, Reverse Recovery (RR), Open-Circuit Voltage Decay (OCVD), Pulsed MOS Capacitor, Other Techniques.
Regards
Laurent ARTOLA
Ph D. Radiation Effects Research Engineer
ONERA - Space environment department
Provided your sample luminesces enough I would recommend time-resolved PL. All the other methods work too but some only work on specific samples and others require background information, like effective mass, dielectric constant, etc. With time-resolved PL, no background knowledge of the sample is needed (other than the PL peak position). In the end though it always depends what equipment your lab has.
One very important distinction for organic solar cells is that they typically use two types of organic semiconductors (a donor and an acceptor) in a bulk heterojunction configuration instead of just one material. As a result, recombination of carriers only occurs at the donor-acceptor interface when you have a bulk heterojunction, and the charge carrier lifetime of the blend can be significantly different than in one of the pure materials. There are a number of studies which have measured and tried to explain the details of the differences and the factors which control the recombination rate (1/lifetime). My recent paper may help you understand these issues more and give additional references about this topic if you want to read more. Please let me know if you have further questions.
Article Nongeminate recombination in neat P3HT and P3HT:PCBM blend films
- Badges
- Science topic
- Similar topics
- Analytical Chemistry
- Column