Verifying Singlet Fission In Pentacene/C₆₀ Solar Cells

In this study, we verified singlet fission in pentacene/C6o solar cells through comparing the experimental and calculated EQE based on the distribution and the diffus ion probability of excitons, in addition, we measured the photocurrent response with the magnetic field.Singlet fission in pentacene/C6o solar cells was verified through comparing the experimental and calculated EQE with the distribution and the diffusion probability of excitons. The best understood fission material to date is pentacene.SF is verified in pentacene by simply measuring the external quantum efficiency (EQE) of a device with a very thick pentacene (ITO/(PEDOT:PSS)(40 nm)/pentacene(600 nm)/(C60)(40 nm)/(Alq3)(8 nm)/Al(100 nm)). A measured EQE of 6.16% at 695 nm is achieved, which is much larger than the maximum calculated EQE (3.45%). The calculation was based on the assumption that all singlet excitons (if SF were not happened) that reached the pentacene-C60 interface contribute to the photocurrent. To estimate the contribution from the direct ionization of pentacene, we fabricated a device (ITO/PEDOT:PSS(40 nm)/pentacene(600 nm)/Alq3(8 nm)/Al) with a single pentacene layer. The EQE at 695 nm was found to be 0.10%, which is negligible. Therefore, the device can attain a maximum EQE of 3.55%, only if the contribution of singlet exciton dissociation at the pentacene-C60 interface and the direct ionization of singlet exciton are taken into account To narrow this discrepancy, only the singlet fission to double the number of excitons can be supposed since the longer singlet diffusion length of 140 nm is not practical in pentacene. Thus, SF in pentacene and the dissociation of triplet excitons at the pentacene-C60 interface are verified. In addition, another thick device with 500 nm thick pentacene showed the similar results. The measured (9.95%) EQE at wavelength of 690 nm was also much larger than the calculated (6.13%) by using the largest singlet diffusion length of 80 nm in the calculation. Indeed, above 350 nm, all the experiments came to the same conclusion as we presented in this study. In this study, pentacene film indicates the coexistence of the thin-film and bulk phases and an antibatic EQE behavior is seen. The maximum EQE is at the wavelength corresponding to the minimum absorption of pentacene.We measured the photocurrent response of the device (ITO/PEDOT:PSS/P3HT/ /pentacene(40 nm)/(C6o)(4O nm)/(Alq3)(8 nm)/Al(100 nm)) with the magnetic field based on the fact that the triplet excitons would be affected by an external magnetic field and found the change of photocurrent response with external magnetic field, thus, singlet fission was verified in pentacene/C60 solar cells.