Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells

Abstract

Solution-processable small molecules for organic solar cells have attracted intense attention for their advantages of definite molecular structures compared with their polymer counterparts. However, the device efficiencies based on small molecules are still lower than those of polymers, especially for inverted devices, the highest efficiency of which is <9%. Here we report three novel solution-processable small molecules, which contain π-bridges with gradient-decreased electron density and end acceptors substituted with various fluorine atoms (0F, 1F and 2F, respectively). Fluorination leads to an optimal active layer morphology, including an enhanced domain purity, the formation of hierarchical domain size and a directional vertical phase gradation. The optimal morphology balances charge separation and transfer, and facilitates charge collection. As a consequence, fluorinated molecules exhibit excellent inverted device performance, and an average power conversion efficiency of 11.08% is achieved for a two-fluorine atom substituted molecule.

Ultrathin Organic Solar Cells with a Power Conversion Efficiency of Over ≈13.0%, Based on the Spatial Corrugation of the Metal Electrode–Cathode Fabry–Perot Cavity

“…The state‐of‐the‐art single‐junction OSCs with plasmonic cavity structures,1, 2, 3 textured light trapping structures,4, 5 multiplasmonic effects,6, 7, 8 morphological implementation,9, 10 bandgap tuning,11, 12 and solution fabrication method13 now provide over 8–11% of power conversion efficiency (PCE) based on the above approaches or a combination of these approaches. However, over the past few years, a serious difficulty has also been observed in the increase of the PCE of single‐junction OSCs to over 12%.…”

Mesogenic complementary absorbing dyads based on porphyrin and perylene units

“…At present, the state-of-the-art power conversion efficiency (PCE) for fullerene-based bulk heterojunction (BHJ) OSCs achieved 11-12% [5][6][7]. In recent years, non-fullerene acceptors have attracted much attention because of their easily tunable molecular energy levels and excellent optical absorption properties [8,9].…”

Indenothiophene-based asymmetric small molecules for organic solar cells

“…3 All the small molecules mentioned above have symmetric structures. At the same time, some examples of asymmetric small molecules were also reported for OSCs by Sharma et al 12 However, the number of asymmetric semiconducting molecules is much less than that of the symmetric counterparts due to less availability of asymmetric p-conjugated cores.…”

“…[5][6][7] So far, the power conversion efficiency (PCE) of single-junction small molecule OSCs has exceeded 11%. 3 For small molecule OSCs, the photoactive layer plays an important role not only in the open circuit voltage (V OC ), but also in the current density, both of which affect the PCE of the resulting device. Therefore, the innovations in active layer materials are attracting more and more attention.…”

“…Although a large number of small molecule donors have been used for OSCs, the building blocks for efficient small molecule donors are limited to few symmetric units such as benzodithiophene, dithienosilole, indacenedithiophene, and diketopyrrolopyrrole. 3,[8][9][10][11] For example, dithienosilole-based (DTS) derivatives were used for small molecule OSCs as donor units, leading to PCEs in the range from 5.8% to over 9%. 9 Wang et al introduced indacenedithiophene-based (IDT) derivatives as donor units to produce a series of high performing small molecules for OSCs.…”