Performance enhancement of poly(3- hexylthiophene): methanofullerene bulk-heterojunction solar cells

L. Jan Anton Koster; Valentin D. Mihailetchi; Jan C. Hummelen; Paul W. M. Blom

doi:10.1117/12.684116

15 November 2006 Performance enhancement of poly(3- hexylthiophene): methanofullerene bulk-heterojunction solar cells

L. Jan Anton Koster, Valentin D. Mihailetchi, Jan C. Hummelen, Paul W. M. Blom

Proceedings Volume 6334, Organic Photovoltaics VII; 633409 (2006) https://doi.org/10.1117/12.684116
Event: SPIE Optics + Photonics, 2006, San Diego, California, United States

Abstract

Using a newly developed device model we have studied the effect of controlled thermal annealing on charge transport and photogeneration in bulk-heterojunction solar cells (BHJ) made from blend films of regioregular poly(3- hexylthiophene) (P3HT) and methanofullerene (PCBM). With respect to the charge transport, we demonstrate that the hole mobility in the P3HT phase of the blend is dramatically affected by thermal annealing. It increases more than three orders of magnitude, to reach a value up to ≈2×10^-8 m²/Vs after the annealing process, as a result of an improved crystallinity of the film. Slow drying leads to an additional 33-fold enhancement of the hole mobility even up to 5.0×10^-
7 m²V^-1s^-1, thereby balancing the transport of electrons and holes in the blend. The resulting reduction of space-charge accumulation enables the use of thick films (~300 nm), absorbing most of the incoming photons, without losses in the fill factor and short-circuit current of the device. As a next step we performed model calculations to exploit the potential of polymer/fullerene bulk heterojunction solar cells. Lowering the polymeric band will lead to a device efficiency exceeding 6%. Tuning the electronic levels of PCBM in such a way that less energy is lost in the electron transfer process enhances the efficiency to values in excess of 8%. Ultimately, with an optimized level tuning, band gap and balanced mobilities polymeric solar cells can reach power conversion efficiencies approaching 11%.

Citation Download Citation

L. Jan Anton Koster, Valentin D. Mihailetchi, Jan C. Hummelen, and Paul W. M. Blom "Performance enhancement of poly(3- hexylthiophene): methanofullerene bulk-heterojunction solar cells", Proc. SPIE 6334, Organic Photovoltaics VII, 633409 (15 November 2006); https://doi.org/10.1117/12.684116

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