In organic photovoltaics, high power conversion efficiencies (PCE) are mostly achieved on device areas well below 0.1 cm2. Herein, organic solar cells based on a D18:Y6 absorber layer on an active area of ≥ 1 cm2 with a certified PCE of 15.24% are reported. The impacts of the sheet resistance of the transparent electrode and the cell design are quantified by means of full optical device simulations and an analytical electrical model. Three imaging methods (light beam‐induced current, dark lock‐in thermography, and electroluminescence [EL]) are applied and reveal a strong homogeneity of the record cell. Nevertheless, it is found that there is substantial room for improvement mostly in current but also in fill factor and that a PCE of 18.6% on ≥1 cm2 is feasible with this absorber material. Further, photoluminescence (PL) and EL spectroscopy reveal that both emissions occur at the same wavelength(s) and are very similar to the PL spectrum of a pure Y6 acceptor film. The latter points strongly toward electronic coupling between the S1 states of the acceptor and the charge transfer states at the donor/acceptor interface.

large-scale production is still hampered by rather low efficiencies in larger areas and also their long-term stability has yet to be demonstrated for devices with high-efficiency absorber materials. The power conversion efficiency of small area lab devices was increased significantly in the last few years and peaks at >18% for cells with a size of < 0.1 cm 2 and >15% for cells with at least 1 cm 2 . [1][2][3][4] Further advancements in efficiency and lifetime required for the commercialization of OPV are to be realized through novel, further improved organic semiconductors in the photoactive layer and improved charge carrier selectivity in the electron and hole transport layers. This must be accompanied by an ever more detailed understanding of the factors actually limiting device performance. Improved understanding is in part achieved through advanced characterization techniques. Among them, photo-and electroluminescence (PL and EL) (spectroscopy) play a crucial role and they already have proven to be very valuable for all types of crystalline inorganic solar cells. This is because, in these types of devices, the luminescence signal originates from the radiative recombination of free electrons and holes and is, therefore, a direct measure of the product of their concentrations within the material from where the emission stems, that is, usually the photoactive layer. However, in the case of organic solar cells, photoluminescence is not straightforward to interpret as the charge generation and recombination processes are more complex in organic absorber materials. In the latter, the absorption of a photon generates a rather strongly bound exciton in the donor or the acceptor phase. Then, the exciton might diffuse to a donor/acceptor interface where it can dissociate into free charge carriers, an electron in the acceptor and a hole in the donor, respectively. Although this works remarkably well as indicated by the high internal quantum efficiencies of high-performing organic solar cells, [28] some of these excitons will decay before they can form free charge carriers. And from those, a certain fraction will do this in a radiative manner, thus emitting luminescence. Important to note here is the fact that the probability for their decay to be radiative is much larger than for free charge carriers that recombine via charge transfer (CT) states at the donor/acceptor interface. [3,[29][30][31][32][33][34][35][36] As a consequence, the PL signal of an organic solar cell is dominatedThe detection of photoluminescence (PL) is an important characterization method for many photovoltaic technologies providing direct information about the separation of the quasi-Fermi levels (QFL), ΔE F . However, for organic solar cells, the PL is dominated by excitons, which decay radiatively before they form free charge carriers via dissociation at donor/acceptor interfaces. This (major) part of the PL signal does therefore not correlate with ΔE F . In contrast, electroluminescence (EL) stems from injected electrons and holes, which recom...

An overshoot of the open‐circuit voltage (V OC) after switching off the illumination is observed for perovskite solar cells, while the simultaneously measured photoluminescence (PL) intensity decreases continuously. Similarly, a dip in the photovoltage transient is detected at the beginning of a light pulse added to a continuous bias light, while the PL increases. This decoupling of external and implied V OC (as derived from the PL data) originates from a strong gradient of the majority charge carrier quasi‐Fermi level in the vicinity of a nonideal contact. This gradient reduces the external voltage much more than the implied voltage. The V OC overshoot is observed whenever the gradient decreases faster than when the separation of the quasi‐Fermi levels is reduced by charge carrier recombination. As shown in previous work, in perovskite solar cells, the magnitude of the gradient is strongly influenced by mobile ionic species and it decreases upon light soaking. This is why a fully light‐soaked device does not show this kind of V OC overshoot.

No abstract