Using Porphyrins in Solar Cells

In this report, we demonstrate that porphyrins with suitable chemical structures can be efficiently used in dye-sensitized solar cells (DSSC) as well as in polymer solar cells.

For DSSC in the near-IR region, a series of new porphyrins (LWP1 - 4) were prepared by attaching pyrene or 4-dimethylaminophenyl group in combination with anthracene to modify the porphyrin core.¹ Significantly, DSSCs adopting the LWP1 dye exhibit energy conversion up to 800 nm without compromising the high overall efficiency. This achievement is attributed to the collective effects of the broadened and red-shifted IPCE spectra, elevated energy level at the excited states of the dyes, proper dye soaking processes, and suitable electron-donating substituent. To further this achievement, we prepared LD31 porphyrin based on LWP3.² The device made of LD31 exhibited panchromatic spectral feature covering the whole visible region and further extending over 800 nm. When combined with an organic dye (AN-4), the performance of the LD31/AN-4 co-sensitized device attained J_sc/mA cm^-2 = 20.3, V_oc/mV = 704, FF = 0.72, and the overall efficiency of power conversion η = 10.3 %.

For porphyrin-incorporated polymer (PPor) solar cells, a pyrene-modified porphyrin was used as a complementary light-harvesting unit (LHU). It was found that adding proper amount of the LHU increased light absorption in the 400-500 nm region, rendering the porphyrin-incorporated D-A copolymers (PPor) panchromatic light absorbers. V_oc-J_sc trade-offs commonly seen in many D-A polymers were not found in the PPors reported in this work. This is attributed to the presence of the LHU increasing the J_sc without sacrificing the V_oc and FF of the polymer solar cells (PSCs). Thus, 8.0% PCE was observed for the PPor-2:PC₇₁BM single-junction PSCs. Significantly, 8.6% PCE was achieved when a C-PCBSD cathodic interlayer was introduced to suppress linkage current.³

References:

1. C.-H. Wu, M.-C. Chen, P.-C. Su, H.-H. Kuo, C.-L. Wang, C.-Y. Lu, C.-H. Tsai, C.-C. Wu,* C.-Y. Lin,* J. Mater. Chem. A, 2014, 2, 991-999.

2. C.-L. Wang, J.-Y. Hu, C.-H. Wu, H.-H. Kuo, Y.-C. Chang, Z.-J. Lan, H.-P. Wu, E. W.-G. Diau,* C.-Y. Lin,* Energy Environ. Sci., 2014, 7, 1392–1396.

3. Y.-H. Chao, J.-F. Jheng, J.-S. Wu, K.-Y. Wu, M.-Ch. Tsai, C.-L. Wang, Y.-N. Hsiao, C.-L. Wang,* C.-Y. Lin,* C.-S. Hsu,* Adv. Mater., 2014, 26, 5205-5210.

Acknowledgment: This work is supported by the Ministry of Science and Technology, Taiwan.