Abstract
The widespread use of nonfullerene-based electron-accepting materials has triggered a rapid increase in the performance of organic photovoltaic devices. However, the number of efficient acceptor compounds available is rather limited, which hinders the discovery of new, high-performing donor:acceptor combinations. Here, we present a new, efficient electron-accepting compound based on a hitherto unexplored family of well-known molecules: gold porphyrins. The electronic properties of our electron-accepting gold porphyrin, named VC10, were studied by UV–Vis spectroscopy and by cyclic voltammetry (CV) , revealing two intense optical absorption bands at 500–600 and 700–920 nm and an optical bandgap of 1.39 eV. Blending VC10 with PTB7-Th, a donor polymer, which gives rise to an absorption band at 550–780 nm complementary to that of VC10, enables the fabrication of organic solar cells (OSCs) featuring a power conversion efficiency of 9.24% and an energy loss of 0.52 eV. Hence, this work establishes a new approach in the search for efficient acceptor molecules for solar cells and new guidelines for future photovoltaic material design.
Highlights
Organic solar cells (OSCs) based on solution-processed bulk heterojunction (BHJ) active layers have emerged as promising solutions for the conversion of solar energy into electrical energy in building and indoor applications due to their unique advantages, such as being lightweight and semitransparent and the possibility of being processed by low-cost roll-to-roll methods.[1−6] A blend of an electron-donating material and an electron-accepting material forms the BHJ active layer, creating internal donor−acceptor heterojunctions, and their optical and electrochemical properties are very important for the realization of a high power conversion efficiency (PCE).[7−9]
Nonfullerene small-molecule acceptors (NFSMAs) have attracted extensive interest due to their promising characteristics, such as easy approachability, better absorption covering both visible and near-infrared (NIR) regions, and tunable frontier energy levels,[19−22] and the PCE of OSCs has reached values in the range of 17−18% for a single junction active layer.[23−27] It was predicted that a PCE greater than 20% can be attained by employing suitable donors and nonfullerene small-molecule acceptors (NFSMAs) in the BHJ active layer and by device optimization,[28−30] with values greater than 26% possible for Received: November 24, 2021
To obtain more information about the recombination processes in the active layer, we examined the variation in JSC and VOC with the illumination intensity (Pin) of the OSCs,[65,66] and this is shown in Figure S18a,b
Summary
Organic solar cells (OSCs) based on solution-processed bulk heterojunction (BHJ) active layers have emerged as promising solutions for the conversion of solar energy into electrical energy in building and indoor applications due to their unique advantages, such as being lightweight and semitransparent and the possibility of being processed by low-cost roll-to-roll methods.[1−6] A blend of an electron-donating material and an electron-accepting material forms the BHJ active layer, creating internal donor−acceptor heterojunctions, and their optical and electrochemical properties are very important for the realization of a high power conversion efficiency (PCE).[7−9]. Porphyrins are planar and highly conjugated macrocycles that play crucial roles in photosynthesis and other biological processes,[32] exhibiting remarkable light-harvesting ability as they absorb light in both the blue and red regions of the visible spectrum Their optical and electrochemical properties can be adjusted by molecular design and functionalization on the β or meso positions of the porphyrin ring as well as by introduction of different central metal ions. Porphyrin-based compounds acting as acceptor units in OSCs are rarely reported, with the connection of strong electron-withdrawing moieties to the electron-donor Zn-porphyrin macrocycle being the strategy adopted.[41] In 2014, two different porphyrin derivatives with two isoindigo as end-capped acceptor units were applied as nonfullerene acceptors in solution-processed solar cells paired with P3HT, and the OSCs showed a PCE of approximately 0.57%.42. TFA, CH2Cl2; (v) KAuCl4/AgOTf/CH3CO2Na, CH2Cl2/THF (70 °C); (vi) KPF6, CH2Cl2/H2O; (vii) 3, Pd2(dba)3/AsPh3, CH2Cl2/MeOH, Et3N (50 °C)
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