shown to reach power conversion efficiencies (PCEs) >10%, [2] the synthesis of π-conjugated polymers with specific optical gaps and little-to-no batch-to-batch variation remains a practical limitation in the scaling-up of high-efficiency polymerfullerene BHJ devices. [3] In parallel, the narrow spectral absorption of fullerene acceptors (e.g., [6,6]-phenyl-C 61 (or C 71 )butyric acid methyl ester, namely, PC 61 BM and PC 71 BM) falling in the short-wavelengths region (≈300-450 nm) inherently limits photonic absorption, since most of the photon flux occurs in the visible range of the solar spectrum (>450 nm). By contrast, all-SM BHJ solar cells can involve two visible light absorbers-, i.e., π-extended SM donor and SM acceptorthus, all-SM devices could in principle produce higher photocurrents and outperform their polymer-fullerene BHJ counterparts. [1g,4] SM materials feature on the properties of being well-defined, size-monodispersed, and scalable. "Nonfullerene" SM acceptors add the benefit of being synthetically accessible in controlled purities, while these may also be readily produced on large scales. Nevertheless, reaching high PCE values with the all-SM device approach has remained challenging thus far, mainly owing to i) morphology limitations prevailing in the absence of polymer (e.g., lack of control over domain sizes, crystallinity, among other important aspects) and ii) the difficulty to reach the enhancement and balance of charge transport in active layers. [3a,4b,5] With the use of processing additives [6] or solvent vapor annealing (SVA)
Solution-processed small molecule (SM) solar cells have the prospect to outperform their polymer-fullerene counterparts. Considering that both SM donors/acceptors absorb in visible spectral range, higher expected photocurrents should in principle translate into higher power conversion efficiencies (PCEs). However, limited bulk-heterojunction (BHJ) charge carrier mobility (<10-4 cm 2 V -1 s -1 ) and carrier lifetimes (<1 µs) often impose active layer thickness constraints on BHJ devices (≈100 nm), limiting external quantum efficiencies (EQEs) and photocurrent, and making largescale processing techniques particularly challenging. In this report, it is shown that ternary BHJs composed of the SM donor DR3TBDTT (DR3), the SM acceptor ICC6 and the fullerene acceptor PC 71 BM can be used to achieve SM-based ternary BHJ solar cells with active layer thicknesses >200 nm and PCEs nearing 11%. The examinations show that these remarkable figures are the result of i) significantly improved electron mobility (8.2 × 10 -4 cm 2 V -1 s -1 ), ii) longer carrier lifetimes (2.4 µs), and iii) reduced geminate recombination within BHJ active layers to which PC 71 BM has been added as ternary component. Optically thick (up to ≈500 nm) devices are
