Highly Efficient Organic Thin-Film Solar Cells Based on Poly(3-hexylthiophene) and Soluble C70 Fullerene Derivative

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The C70 derivative [6,6]-phenyl-C71-butyric acid methyl ester ([70]PCBM) has wider and stronger absorption in the visible light region than the analogous C60 derivative ([60]PCBM). Using [70]PCBM as an n-type semiconductor in combination with poly(3-hexylthiophene) (P3HT), we successfully fabricated a highly efficient organic photovoltaic (PV) cell showing higher short-circuit current density ($J_{\text{SC}}$) and incident photon-to-electron conversion efficiency (IPCE) values than a P3HT:[60]PCBM-blend cell, with a maximum power conversion efficiency ($\mathit{PCE}$) of 3.8% under standard simulated solar illumination (air mass 1.5 G, 100 mW/cm2). All of the PV characteristics of the P3HT:[70]PCBM and P3HT:[60]PCBM cells were identically improved by thermal annealing, suggesting that changes in the internal structure of the photovoltaic layer and in the contact between the photovoltaic layer and the top electrode of the P3HT:[70]PCBM cell occurred in a similar manner to those of the P3HT:[60]PCBM cell. Therefore, [70]PCBM is an easy-to-replace alternative n-type semiconducting molecule to [60]PCBM, which has a higher $\mathit{PCE}$.
2008-02-25