| AVS 58th Annual International Symposium and Exhibition | |
| Energy Frontiers Focus Topic | Wednesday Sessions |
| Session EN+NS-WeM |
| Session: | Organic Photovoltaics |
| Presenter: | Marc Baldo, Massachusetts Institute of Technology |
| Authors: | P. Jadhav, Massachusetts Institute of Technology A. Mohanty, Massachusetts Institute of Technology J. Sussman, Massachusetts Institute of Technology M. Baldo, Massachusetts Institute of Technology |
| Correspondent: | Click to Email |
Singlet exciton fission is a process by which a high energy singlet spontaneously decomposes into two low energy triplets. It is an example of a multi-exciton generation process that could allow the efficiency of solar cells to reach beyond the Shockley-Quiesser limit. In this talk we examine singlet exciton fission in solar cells based on tetracene and diphenyltetracene (DPT). Notably we find that the photocurrents in each cell have opposite dependencies on the application of a magnetic field, suggesting that fission increases the photocurrent in tetracene-based solar cells, but decreases the photocurrent in DPT-based solar cells.
We report an organic semiconductor solar cell using tetracene and CuPC (Copper Phthalocyanine) as donors, and C60 as the acceptor. Tetracene absorbs photons in the 450-550-nm region, generating high energy singlets which split into two lower energy triplets, potentially doubling the photocurrent in this part of the spectrum. CuPC extends the absorption of the solar cell to the red part of the spectrum. We also demonstrate bulk heterostructure tetracene-C60 devices and tested them for singlet exciton fission.
We observe that: (i) The addition of the CuPC layer does not affect the flow of excitons from tetracene to the CuPC – C60 junction significantly because of similarities in triplet energies of tetracene and CuPC, (ii) The application of a .5T magnetic field shows ~-1.5% change in photocurrent, confirming singlet fission, (iii) Low temperature quantum efficiency measurements show a drop in the tetracene IQE (internal quantum efficiency), and a singlet fission yield of 72% at room temperature. The drop in performance at low temperature is expected since singlet exciton fission in tetracene is a thermally activated process.(iv) Singlet exciton fission has a very high yield even in bulk heterostructure devices and can be potentially used to improve the performance of polymer solar cells.
In comparison, we observe that solar cells consisting of DPT-C60 exhibit a large positive (+5%) effect of the magnetic field on the photocurrent, +5% at ~.4T. We explain the anomalous magnetic field effect and demonstrate that it can be increased beyond 100% by biasing the device close to open circuit, potentially leading to applications as an anisotropic magnetic field detector.