Sylvester-Hvid, K.O.K.O.Sylvester-HvidZiegler, T.T.ZieglerRiede, M.K.M.K.RiedeKeegan, N.N.KeeganNiggemann, M.M.NiggemannGombert, AndreasAndreasGombert2022-03-032022-03-032007https://publica.fraunhofer.de/handle/publica/21361710.1063/1.27752192-s2.0-34548622739A nondestructive method for assessing the thickness of the photoactive layer in poly(3-hexyl-thiophene):1-(3-methoxy-carbonyl)propyl-1-phenyl-(6,6)C-61 (P3HT:PCBM) solar cells is reported. In the approach the absorption spectrum of the solar cell as derived by optical simulations is fitted to the corresponding measured spectrum, varying only the P3HT:PCBM layer thickness. Within the 50-250 nm thickness range, a linear correlation between the position of a certain spectral minimum and the P3HT:PCBM layer thickness is shown, based on simulated absorption spectra. As an initial application, absorption spectra for 240 P3HT:PCBM solar cells prepared at four different spin-coating speeds were recorded, and the average P3HT:PCBM layer thickness estimated for each spin-coating speed. The simulated fraction of light absorbed in the P3HT:PCBM layer of the solar cells is compared with the P3HT:PCBM absorption spectra measured for films spin coated on simpler substrate types. The latter spectra cannot account for the light harvested in the photoactive layer of P3HT:PCBM solar cells because of substantial optical interference in the solar cells. The measured short circuit current densities J(sc) for the solar cells vary with the spin-coating speed in a manner confirmed by optical simulations of the maximal short circuit current densities. The measured efficiencies follow the same pattern. On average the measured J(sc) is 1-2 mA/cm(2) below the simulated maximal short circuit current densities. Based on the resemblance of the measured and simulated absorption spectra such difference can be attributed to recombination exclusively.en621697530journal article