Influence of p-type and n-type semiconductor composition ratio on open circuit voltage in bulk hetero junction organic solar cells
Kazuhiro Komatsu a, Shogo Mori a b
a Graduate School of Science and Technology, Shinshu university, Ueda,Nagano 386-8567, Japan
b Center for Energy and Environmental Science, Shinshu University, 4-17-1 Wakasato, Nagano, 380-8553, Japan
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics (AP-HOPV17)
Yokohama-shi, Japan, 2017 February 2nd - 4th
Organizers: Tsutomu Miyasaka and Iván Mora-Seró
Poster, Kazuhiro Komatsu, 021
Publication date: 7th November 2016

Open circuit voltage (Voc) of organic solar cells is determined by the difference between the Fermi level of the p-type and the n-type semiconductor. This Fermi level difference is varied with the relative energy levels between p and n type materials and the charge densities, which is related with charge recombination rate. These relative energy and recombination rate are affected by the structure of solar cells. Thus, thermal annealing, film thickness, and semiconductor composition ratio of the active layer film can affect the Voc. Especially, the semiconductor composition ratio has large influence. Thus, the aim of this study is, to clarify the origin of the effect of composition ratio on Voc. We used poly(3-hexylthiophene) (P3HT) as a donor and phenyl-C61-butylic acid methyl ester (PCBM) as an acceptor materials. We prepared solar cells with the composition ratio of P3HT: PCBM = 3:1, 2:1, 1:3. Charge recombination and, charge density were measured by a modified charge extraction method using a fast switch and reverse bias under extraction. As a result, the Voc of 1:3 cells was the highest under 1 sun conditions. When Voc was compared among the cells with different ratios at the same charge density, the cells with 1:3 had the highest Voc. This suggests the difference of the energy levels between P3HT and PCBM was the highest among the cells.

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