The maximum photocurrent in tandem organic solar cells (TOSCs) is often obtained by increasing the thicknesses of sub-cells, which leads to recombination enhancement of such devices and compromises their power conversion efficiency (PCE). In this work, an efficient interconnecting layer (ICL) is developed, with the structure ZnO NPs:PEI/PEI/PEDOT:PSS, which enables TOSCs with very good reproducibility. Then, it is discovered that the optimal thickness of the front sub-cell in such TOSCs can be reduced by increasing the proportion of a non-fullerene acceptor in the active layer. The non-fullerene acceptor used in this work has a much larger absorption coefficient than the donor in the front sub-cell, and the absorption reduction of donor can be well complemented by that of the acceptor when increasing the acceptor proportion, thus leading to a significant overall absorption enhancement even with a thinner film. As a result, the optimal thickness of the front sub-cell is reduced and its charge recombination is suppressed. Ultimately, the use of this ICL combined with fine-turning of the composition in the front sub-cell enables an efficient TOSC with a very high fill factor of 78% and an excellent PCE of 18.71% (certified by an accredited institute to be 18.09%) to be obtained.
Random conjugated polymers, such as typical polymerized small molecular acceptors (PSMAs), concurrently suffer from the dual batch factors of molecular weights (MWs) and regioregularity, which seriously interfere with the study of the relationship between batch factors and polymer properties. Here, four isomer‐free PSMAs, PA‐5 and three members of a PA‐6 series with low (L), medium (M), and high (H) MWs, in which 5 and 6 define linkage position throughout conjugated backbone, are designed and synthesized to clearly investigate polymer batch effects. These studies reveal that PA‐6‐L and PA‐6‐M have ignorable batch differences within deviations, which deliver comparable maximum efficiencies of 14.81% and 14.99%, respectively. The PA‐6‐H based cell is processed from chlorobenzene with its high boiling point, due to the limited solubility in other common solvents, leading to large‐size phase separation during prolonged film drying process, and thereby inferior performance. In contrast, PA‐5 possesses diverse absorption characteristics, and ordered crystallization, which prompts higher short‐circuit current density and fill factor in the cell. As a result, the corresponding device realizes a photovoltaic performance of 16.11%, which is one of the best binary all‐polymer solar cells in the reported literature to date. This study provides a new insight into complicated batch effects of PSMAs on device performance while avoiding cross‐talk between them.
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