Burn-In Degradation Mechanism Identified for Small Molecular Acceptor-Based High-Efficiency Nonfullerene Organic Solar Cells

Abstract

Organic solar cells (OSCs) have again become a hot research topic in recent years. The record power conversion efficiency (PCE) of OSCs has boosted to over 17% in 2020. Apart from the high PCE, the stability of OSCs is also critical for their future applications and commercialization. Recently, many studies have proposed that burn-in degradation can be considered as an ineluctable barrier to long-term stable OSCs. However, there is still lack of studies to explain the detailed mechanism of this burn-in process. In this work, we first investigated the mechanism of the burn-in process in the high-efficiency PM6:N3-based nonfullerene OSCs. The PM6:N3-based device achieved a profound average PCE of 14.10% but also showed a significant performance loss after the burn-in degradation. Following characterizations such as dark J−V, photoluminescence (PL), time-resolved PL, Urbach energy estimation, and electrochemical impedance spectroscopy reveal that the burn-in degradation observed is closely related to the current extraction, energy transfer, nonradiative recombination, and charge transport process in the PM6:N3-based device. At the same time, it has small effects on the exciton dissociation process and energetic disorder in the PM6:N3-based device. Atomic force microscopy, scanning electron microscopy, transmission electron microscopy, and grazing incidence X-ray diffraction measurements gratifyingly found that the morphology of the PM6:N3 active layer is relatively stable during the burn-in degradation. Therefore, these observed degradations are suspected results from the instability of interfaces and electrodes. The atoms in carrier transport layers and electrodes may diffuse to the active layer during the degradation, which changes the energy levels of each layer and causes traps at the interface and in the active layer. Conquering the instability of interfaces and electrodes is proposed as the prior task for PM6:N3-based OSCs to achieve long-term stability. Our study provides insights into the mechanism behind the burn-in degradation of the PM6:N3-based OSCs, which takes the first step to conquer this barrier.

A Non‐Conjugated Polymer Acceptor for Efficient and Thermally Stable All‐Polymer Solar Cells

“…As shown in Figure 3, the IDIC16‐based PSC shows poor thermal stability and dramatically decreased PCE even after 1 h under a continuous thermal storage of 85 °C. Moreover, it only retained ≈50 % of its initial PCE when stored at 85 °C for only 18 h. On the contrary, the PF1‐TS4‐based all‐PSC presents outstanding thermal stability and still retained ≈70 % of its initial PCE after being stored at 85 °C for 180 h. It was noticed that the all‐PSC exhibits a major drop in PCE during the first 30 hours annealing, which is due to the so called burn‐in degradation caused by the instability of interfaces and electrodes [42] . Furthermore, the IDIC16‐based PSC shows a much larger drop in PCE than the PF1‐TS4‐based all‐PSC, which may be attributed to the combination of burn‐in degradation and poor morphological stability of its active layer (discussed right below).…”

A Non‐Conjugated Polymer Acceptor for Efficient and Thermally Stable All‐Polymer Solar Cells

“…Moreover, it only retained % 50 % of its initial PCE when stored at 85 8C for only 18 h. On the contrary, the PF1-TS4-based all-PSC presents outstanding thermal stability and still retained % 70 % of its initial PCE after being stored at 85 8C for 180 h. It was noticed that the all-PSC exhibits a major drop in PCE during the first 30 hours annealing, which is due to the so called burn-in degradation caused by the instability of interfaces and electrodes. [42] Furthermore, the IDIC16-based PSC shows a much larger drop in PCE than the PF1-TS4-based all-PSC, which may be attributed to the combination of burn-in degradation and poor morphological stability of its active layer (discussed right below). To understand the thermal stability difference between these two devices, atomic force microscopy (AFM) and transmission electron microscopy (TEM) measurements were performed to study their active layer morphologies (Figure 4).…”

Interface Modification Enabled by Atomic Layer Deposited Ultra‐Thin Titanium Oxide for High‐Efficiency and Semitransparent Organic Solar Cells

“…Our previous study has reported the burn‐in degradation of the control device, where the unencapsulated device showed around 50% of PCE loss after the burn‐in test for 5 h, as also shown in Figure 8a. [ 20 ] In this study, the unencapsulated two TiO x ALD cycles modified device showed improved device stability compared with the control device. It was found that the J sc and FF of the device decreased by around 10% and 20%, respectively, which contributed to the 30% degradation in PCE.…”

“…[ 18,19 ] We have previously reported a 14% PCE for the N3‐based OSCs in an inverted device structure based on the ZnO layer. [ 20 ] The unencapsulated device showed around 50% of PCE loss after the burn‐in degradation test for 5 h, where the instability of the interface layers and the electrode was found to be the leading cause. Herein, modifying the ZnO layer can be a feasible method to bring further performance and stability improvement to this type of device.…”