Abstract
The choice of interfacial materials and their properties play a critical role in determining solar cell performance and stability. For compatibility with roll-to-roll printing, it is desirable to develop stable cathode interface layers (CILs) that can be processed over the photoactive layer using orthogonal solvents. In this study, an n-type naphthalene diimide core and oligo (ethylene glycol) side-chain-based conjugated polymer is reported as a universal, efficient CIL for organic and perovskite photovoltaics. Besides good thermal stability and easy processing in alcohol/water, the new CIL is found to possess electron transport properties with an electrical conductivity of 2.3 × 10–6 S cm–1, enabling its use as a CIL with a film thickness of up to ∼35(±2) nm. Utilizing the new CIL, 16% power conversion efficiency (PCE) is achieved for organic solar cells (OSCs) based on the PM6-Y6 photoactive layer (8.9% PCE for no CIL and 15.1% with state-of-the-art CIL, PDINO), and perovskite solar cells from methylammonium lead iodide yielded a PCE of 17.6%. Compared to the reference devices, the new CIL reduced trap-assisted carrier recombination and increased the built-in potential by 80 mV, simultaneously enhancing all photovoltaic parameters. Moreover, new CIL based devices had better photostability with no burn-in losses.
Highlights
The field of organic solar cells (OSCs) has witnessed tremendous progress over the past two decades owing to their immense potential to be lightweight, solution-processable, mechanically flexible and their ability to be semitransparent.[1]
The branched oligo(ethylene glycol) (OEG) side-chain substituted naphthalene diimide (NDI) monomer was synthesized to obtain a desirable solubility of the polymer in the polar target solvents
Exhibited a power conversion efficiency (PCE) of 13.3% (Figure S17, Table S1), comparable to the previously reported PCE for PM6:ITIC-4Cl devices.[45]. This further demonstrates that P2G is a versatile cathode interface layers (CILs) which is compatible with a range of different nonfullerene acceptor (NFA) materials, which are sensitive to chemical interactions with the CILs.[46,47]
Summary
The field of organic solar cells (OSCs) has witnessed tremendous progress over the past two decades owing to their immense potential to be lightweight, solution-processable, mechanically flexible and their ability to be semitransparent.[1]. Light intensity-dependent Voc measurements (Figure 4b) show that the devices with P2G exhibit reduced trap-assisted recombination, as the slope calculated for PDINO and P2G was 1.46 and 1.38 kTq−1, respectively This could account for the relatively higher FF values observed for devices incorporating P2G as the CIL. P2G based devices were found to have improved diode properties (Figure S15), exhibiting lower leakage currents and higher rectification, which could be attributed to the electron selective contact of P2G with the active layer and potentially a more conformal coverage compared to a small molecule film. OSCs with a PM6:ITIC-4Cl BHJ blend incorporating a P2G CIL exhibited a PCE of 13.3% (Figure S17, Table S1), comparable to the previously reported PCE for PM6:ITIC-4Cl devices.[45] This further demonstrates that P2G is a versatile CIL which is compatible with a range of different NFA materials, which are sensitive to chemical interactions with the CILs.[46,47]. On the basis of the above findings, it is evident that P2G can be successfully applied as a versatile CIL to OSCs as well as hybrid perovskite solar cells and consistently deliver significant improvements to the device performance
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