From Event: SPIE Organic Photonics + Electronics, 2017
The initial steps in organic photovoltaic cell (OPV) operation involve the formation of neutral excitons through photo absorption, exciton diffusion to and separation into free charges at the donor acceptor interface.1, 2As the usable solar spectrum spans a large range from the visible to the infra-red (IR), an obvious direction for improved light harvesting is to synthesize donor and acceptor materials with complementary absorption. In such devices, specifically those involving polymer donors and small molecule acceptors, both charge transfer from donor and acceptor moieties, and energy (exciton) transfer from high band gap to low band gap material are possible. Here we show that when charge and exciton transfer processes are present, the co-existence of excitons in both domains can cause a loss mechanism. Charge separation of excitons in a low band-gap polymer is hindered due to exciton population in the larger band-gap acceptor domains. Our results further show that excitons in the lower bandgap material should have a relatively long lifetime compared to the transfer time of excitons from the higher band gap material, in order to contribute to the charge separation. These observations provide significant guidance for design and development of new materials in OPV applications.
Kenan Gundogdu, Harald W. Ade, Bhoj Gautam, He Yan, Robert Younts, and Shangshang Chen, "Impact of exciton transfer dynamics on charge generation in polymer/nonfullerene solar cells (Conference Presentation)," Proc. SPIE 10363, Organic, Hybrid, and Perovskite Photovoltaics XVIII, 103630M (Presented at SPIE Organic Photonics + Electronics: August 09, 2017; Published: 19 September 2017); https://doi.org/10.1117/12.2276020.5581151953001.
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