Abstract
Unveiling the correlations among molecular structures, morphological characteristics, macroscopic properties and device performances is crucial for developing better photovoltaic materials and achieving higher efficiencies. To achieve this goal, a comprehensive study is performed based on four state-of-the-art non-fullerene acceptors (NFAs), which allows to systematically examine the above-mentioned correlations from different scales. It’s found that extending conjugation of NFA shows positive effects on charge separation promotion and non-radiative loss reduction, while asymmetric terminals can maximize benefits from both terminals. Another molecular optimization is from alkyl chain tuning. The shortened alkyl side chain results in strengthened terminal packing and decreased π-π distance, which contribute high carrier mobility and finally the high charge collection efficiency. With the most-acquired benefits from molecular structure and macroscopic factors, PM6:BTP-S9-based organic photovoltaics (OPVs) exhibit the optimal efficiency of 17.56% (certified: 17.4%) with a high fill factor of 78.44%, representing the best among asymmetric acceptor based OPVs. This work provides insight into the structure-performance relationships, and paves the way toward high-performance OPVs via molecular design.
Highlights
Unveiling the correlations among molecular structures, morphological characteristics, macroscopic properties and device performances is crucial for developing better photovoltaic materials and achieving higher efficiencies
A comprehensive landscape covering from molecular design, morphological characteristics, macroscopic properties to photovoltaic parameters was presented, and the organic photovoltaics (OPVs) device based on PM6:BTP-S9 blend exhibited the best performance of 17.56% due to the balance of macroscopic properties as originated from the molecular structure and morphological factors
We found that all non-fullerene acceptors (NFAs) films demonstrated a long exciton lifetime of ~1 ns (0.88 ns for BO-4Cl, 0.86 ns for BTP-S7, 0.92 ns for BTP-S8, 0.83 ns for BTP-S9)
Summary
Unveiling the correlations among molecular structures, morphological characteristics, macroscopic properties and device performances is crucial for developing better photovoltaic materials and achieving higher efficiencies. To push OPVs toward a higher efficiency, it’s necessary to build the structure-performance correlations among molecular structures, morphological characteristics (e.g., molecular packing and phase separation), macroscopic factors (e.g., carrier mobility, charge recombination, and exciton behaviors), and the device performances For this purpose, NFAs with delicately tailored molecular structures should be designed to perform the systematic studies. Four NFA systems with two symmetric NFAs of BO-4Cl and BTP-S7 and two asymmetric NFAs of BTP-S8 and BTP-S9 (Fig. 1a), which belong to the state-of-the-art Y-series molecules, were designed and synthesized to systematically study the structure-performance relationships in OPVs. the effects of extending conjugation, molecular symmetry, and alkyl chain tuning of NFAs on morphological characteristics, macroscopic properties, and photovoltaic parameters were studied and compared. A comprehensive landscape covering from molecular design, morphological characteristics, macroscopic properties to photovoltaic parameters was presented, and the OPV device based on PM6:BTP-S9 blend exhibited the best performance of 17.56% due to the balance of macroscopic properties as originated from the molecular structure and morphological factors
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