Rational Strategy to Stabilize an Unstable High‐Efficiency Binary Nonfullerene Organic Solar Cells with a Third Component

Abstract

decades, heuristic approaches have been successfully used to enhance the performance of OSCs, including synthesis of new donor and acceptor molecules, [5][6][7][8][9][10] optimization of the interface and morphology, [11][12][13][14][15] ternary blending, [16][17][18][19] and device engineering. [20][21][22][23] As a result, power conversion efficiency (PCE) of OSCs has surpassed 15% for single-layer bulkheterojunction systems. [24,25] As the PCE of OSCs is getting closer to the requirements for commercial applications and competing technology, the most efficient OSCs also need to perform consistently or maintain low efficiency loss throughout their lifetimes. [26][27][28] To make organic photovoltaics commercially viable and competitive, researchers have been making efforts on characterizing, understanding, and rationally engineering the long-term stability of OSC devices. [26,[29][30][31][32][33][34][35][36][37][38] Generally, the performance degradation of OSCs comes from the oxidation of electrodes, degradation of the interface layers, and changes in the morphology of the active layer. Among these factors, the oxidation of electrodes and the degradation of the interface layers are attributed to exposure to oxygen and moisture, [39,40] and these drawbacks can be largely prevented by encapsulation. [41,42] However, the intrinsic instability of active layer morphology driven by light, temperature, and thermodynamics cannot be prevented by encapsulation. In-depth studies were carried out to understand the stability of the active layers under multiple stresses. [43] For instance, McGehee and co-workers [29] reported that solar cells based on amorphous materials would suffer from open-circuit voltage (V OC ) burnin degradation resulted from the impact of light-induced traps, and this degradation can be reduced by using materials with high degree of crystallinity. Brabec group [33] demonstrated that the light-induced [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) dimerization would lead to the short-circuit current density (J SC ) loss after aging, while this dimerization can be inhibited by a high degree of polymer-fullerene mixing and it can also be reduced via increasing the crystallization of the fullerene domains. Brabec and co-workers [34] found that burnin degradation driven by low miscibility is the major short-time Long device lifetime is still a missing key requirement in the commercialization of nonfullerene acceptor (NFA) organic solar cell technology. Understanding thermodynamic factors driving morphology degradation or stabilization is correspondingly lacking. In this report, thermodynamics is combined with morphology to elucidate the instability of highly efficient PTB7-Th:IEICO-4F binary solar cells and to rationally use PC 71 BM in ternary solar cells to reduce the loss in the power conversion efficiency from ≈35% to <10% after storage for 90 days and at the same time improve performance. The hypomiscibility observed for IEICO-4F in PTB7-Th (below the percolation threshold) leads to overpurific...

A Universal Method to Enhance Flexibility and Stability of Organic Solar Cells by Constructing Insulating Matrices in Active Layers

“…[ 17,18 ] Thermal‐induced morphological instability due to diffusion, aggregation, or crystallization of organic photovoltaic molecules remains the central driving forces in devices. [ 17,19–22 ] On the other hand, the present OSCs based on small molecular acceptors (SMAs) exhibit high PCEs, while having relative poor flexibility (stretchability) due to brittle crystalline features of the SMAs. [ 4,23 ] However, all‐polymer solar cells with excellent flexibility (stretchability) exhibit limited PCEs, [ 24,25 ] which lag behind the SMAs‐based OSCs.…”

Novel Bimodal Silver Nanowire Network as Top Electrodes for Reproducible and High‐Efficiency Semitransparent Organic Photovoltaics

“…The chemical structures of the blend materials are shown in Figure 2d. The blend exhibits high performance for the opaque cells with the champion efficiency exceeding 11% fabricated in our lab, [ 55 ] with performance often depending on the quality of the PTB7‐Th batch. More importantly, PTB7‐Th:IEICO‐4F blends exhibit strong NIR light harvesting with weak visible absorption.…”

Balanced Charge Transport Optimizes Industry‐Relevant Ternary Polymer Solar Cells

“…Previous works already showed an improved photostability of ternary blends comprising PC 61 BM or PC 71 BM as coacceptor. [ 28,45,46 ] Stability is a complex issue though, and the primary reasons for binary device degradations are often related to the overpurification of the mixed domains or crystallization of the acceptor. [ 47–50 ] In this system, PC 61 BM phase strongly separates from the PTQ10; the mechanism for stabilization would have to be different than countering the overpurification of the mixed domains.…”