An Electron Acceptor Analogue for Lowering Trap Density in Organic Solar Cells

Abstract

Typical organic semiconductor materials exhibit a high trap density of states, ranging from 1016 to 1018 cm−3, which is one of the important factors in limiting the improvement of power conversion efficiencies (PCEs) of organic solar cells (OSCs). In order to reduce the trap density within OSCs, a new strategy to design and synthesize an electron acceptor analogue, BTPR, is developed, which is introduced into OSCs as a third component to enhance the molecular packing order of electron acceptor with and without blending a polymer donor. Finally, the as‐cast ternary OSC devices employing BTPR show a notable PCE of 17.8%, with a low trap density (1015 cm−3) and a low energy loss (0.217 eV) caused by non‐radiative recombination. This PCE is among the highest values for single‐junction OSCs. The trap density of OSCs with the BTPR additives, as low as 1015 cm−3, is comparable to and even lower than those of several typical high‐performance inorganic/hybrid counterparts, like 1016 cm−3 for amorphous silicon, 1016 cm−3 for metal oxides, and 1014 to 1015 cm−3 for halide perovskite thin film, and makes it promising for OSCs to obtain a PCE of up to 20%.

Boosting photovoltaic performance of ternary organic solar cells by integrating a multi-functional guest acceptor

“…2a and the detailed photovoltaic parameters are provided in Table 1. The PM6:Y6 binary control device shows a PCE of 15.64% with a V oc of 0.846 V, a J sc of 26.37 mA/cm 2 , and a fill factor (FF) of 70.30%, which is comparable with the reported values [10,17,43]. On the other hand, the binary OSC based on PM6 and Y-T exhibits a poor PCE of 5.06% and a remarkably high V oc of 1.19 V, resulting from the smaller energetic offset but mismatched HOMO levels between electron donor and acceptor.…”

“…One of the molecular design considerations for achieving favorable morphology in ternary systems is to retain similar backbone structures for both the guest and host acceptors, which is more preferable for the formation of well-mixed alloy states and beneficial for improving charge carrier separation, transport, and correspondingly J sc [38][39][40][41][42]. In addition, this similarity in the acceptors' chemical skeleton has also been shown to effectively reduce trap density in ternary OSCs [43]. In the state-of-the-art PM6:Y6 system, a few Y6 derivatives have been developed as the guest acceptor to achieve improved device performance [40][41][42].…”

Regioregular Narrow‐Bandgap n‐Type Polymers with High Electron Mobility Enabling Highly Efficient All‐Polymer Solar Cells

“…Note that both the LUMO and the HOMO energy levels of MBTI are between those of PM6 and L15, forming a cascade‐like alignment, which facilitates charge transport and transfer in the ternary blend. [ 35,36 ] In addition, L15 and L14 have deeper HOMO/LUMO energy levels compared to those of MBTI due to more electron‐deficient of benzothiadiazole core in Y‐Br than benzodithiophene in M‐Br.…”

Reducing Limitations of Aggregation‐Induced Photocarrier Trapping for Photovoltaic Stability via Tailoring Intermolecular Electron–Phonon Coupling in Highly Efficient Quaternary Polymer Solar Cells

“…To evaluate the distribution of density of state (DOS) for trap states at the device level, we performed the capacitance spectroscopy measurements on BHJ/LbL‐type binary and quaternary OSCs with or without thermal aging treatment in dark (Figures S25 and S26, Supporting Information). The measured capacitance‐frequency spectra have been transformed into the energetic profiles of trap DOS through Mott–Schottky characterization and the related Gaussian shape distribution of trap DOS can be described in the following expression [ 52–54 ] where σ represents the disorder parameter, E t is the energy center of trap DOS, and N t is the total density per unit volume. Detailed fitting results are displayed in Figure 5v and Figure S28 as well as Table S17 in the Supporting Information.…”