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We studied fullerene-free organic solar cells using rhodanine-terminated BDT3TR and O-IDTBR.

Solar energy is widely regarded as a highly efficient and sustainable source for future energy harvesting. In particular, organicinorganic hybrid perovskite solar cells (PeSCs), which exhibit remarkable power conversion efficiencies (PCEs) exceeding 22% [1] and unique optoelectronic properties, [1c,2] have attracted considerable interest as the most promising materials for large-scale solar energy conversion. [3] In general, the morphology and crystallinity of organic-inorganic halide perovskite films are considered to be crucial to both the efficiency and the stability of PeSCs. [4] Large-sized, highly crystallized, and preferentially oriented perovskite grains provide good surface coverage and a small grain boundary area, which effectively minimize not only the presence of pinholes but also the trapping and recombination of charge carriers. [5] In this respect, considerable effort has been devoted toward preparing high-quality perovskite films with large-sized grains for significantly improving the device performance of PeSCs. [6] Among the various approaches for increasing the perovskite grain size, the addition of chemical additives, such as hypophosphorous acid, [7] methylammonium chloride, [8] 1,8-diiodooctane, [9] urea, [10] and lead thiocyanate (Pb(SCN) 2 ), [11] is widely adopted as it can exploit simple low-temperature processes (typically <150 °C) desirable for effective continuous processing. [12] Although such additive engineering remarkably increases the perovskite grain size to the micrometer scale under extremely mild conditions, the inherent insulating property of the additives prevents the efficient extraction and transport of charge carriers in the perovskite layers, [13] thereby limiting the applicability of this approach.In this paper, we report a semiconducting organic conjugated molecule (SA-1) as a novel chemical additive that increases the grain size of perovskite films without hindering the charge transport and thus improves the device performance considerably (Figure 1a-c). Experimental and analytical investigations revealed that the addition of SA-1 remarkably increased the perovskite grain size through a Lewis acid-base interaction and facilitated charge transport and extraction in the perovskite layer owing to suitable energy level matching and high charge The addition of chemical additives is considered as a promising approach for obtaining high-quality perovskite films under mild conditions, which is essential for both the efficiency and the stability of organic-inorganic hybrid perovskite solar cells (PeSCs). Although such additive engineering yields high-quality films, the inherent insulating property of the chemical additives prevents the efficient transport and extraction of charge carriers, thereby limiting the applicability of this approach. Here, it is shown that organic conjugated molecules having rhodanine moieties (i.e., SA-1 and SA-2) can be used as semiconducting chemical additives that simultaneously yield large-sized perovskite grains and improve the charge extr...

Solution‐processed organic solar cells are promising owing to their light weight, ease of processability, low cost, flexibility, and large‐area fabrication. Particularly, small‐molecule active materials have been recently developed using straightforward synthesizing methods, exhibiting the least batch‐to‐batch variation in physical and optoelectronic properties and highly reproducible efficiency. A series of 2D‐BDT‐based active materials with various numbers of benzodithiophene (BDT) units and how the number of 2D‐BDT units influences the construction of a well‐defined interconnected structure are reported. The systematically controlled morphology of the 2D‐BDT material helps achieve a high power‐conversion efficiency (PCE) of 8.56% and a high fill factor of 0.73 without the use of additives. The reduced charge recombination and well‐constructed morphology of this material facilitate a PCE of 7.45% in a 77.8 cm2 rigid module, which is the outstanding performance in large‐area modules.