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Water/alcohol soluble cathode interfacial materials (CIMs) are playing important roles in optoelectronic devices such as organic light emitting diodes, perovskite solar cells and organic solar cells (OSCs). Herein, n-doped solution-processable single-wall carbon nanotubes (SWCNTs)-containing CIMs for OSCs are developed by dispersing SWCNTs to the typical CIMs perylene diimide (PDI) derivatives PDIN and PDINO. The Raman and X-ray photoelectron spectroscopy (XPS) measurement results illustrate the n-doped behavior of SWCNTs by PDIN/PDINO in the blend CIMs. The blended and n-doped SWCNTs can tune the work function and enhance the conductivity of the PDI-derivative/SWCNT (PDI-CNT) composite CIMs, and the composite CIMs can regulate and down-shift the work function of cathode, reduce the charge recombination, improve the charge extraction rate and enhance photovoltaic performance of the OSCs. High power conversion efficiency (PCE) of 17.1% and 17.7% are obtained for the OSCs based on PM6:Y6 and ternary PM6:Y6:PC71BM respectively with the PDI-CNT composites CIMs. These results indicate that the n-doped SWCNT-containing composites, like other n-doped nanomaterials such as zero dimensional fullerenes and two dimensional graphenes, are excellent CIMs for OSCs and could find potential applications in other optoelectronic devices.

Three alcohol-soluble nonconjugated polymers poly [p-(N,N-dimethylamino)styrene] (PSN), poly[p-(N,N-dimethylamino)styrene] oxide (PSO), and poly[p-(N,N-dimethylamino)styrene] mesylate (PSM) were devised and synthesized for the application as cathode interlayers in the organic solar cells (OSCs) based on PBDB-T:IT-M. All of the polymers contain a highly polarized amino or ammonium group at the side chains, which can improve electron collection ability of the cathode interfacial layer of the OSCs. Both the amino and ammonium group with a negative ion of oxygen allow PSN and PSO to possess intermolecular n-doping effect with the IT-M acceptor at the interface. The understanding of the relationship between the n-doping effect and the cathode interlayer structures may offer additional insights to further develop novel cathode interfacial materials for OSCs.

Interface engineering is a critical factor in achieving high photovoltaic performances for large-area, printable, flexible and low cost organic solar cells (OSCs). Herein, we developed a solution-processable n-doped graphene cathode interfacial material (CIM) PDINO–G for OSCs by adding graphene to the classic material PDINO ((N,N-dimethyl-ammonium N-oxide)propyl perylene diimide). The dispersed graphene in PDINO–G was n-doped by the nitroxide radical of N-oxide in PDINO, which was certified by the ESR, Raman spectroscopy and XPS results. The n-doped PDINO–G CIM possessed increased conductivity, lower work function, reduced charge recombination and increased charge extraction rate. Previously, n-doped graphene was prepared only on the surface of chemical vapor-deposited (CVD) graphene films without solution processability. The effect of the CIM on the photovoltaic performance of OSCs was studied by selecting the photovoltaic model system of PTQ10 as the donor and IDIC-2F as the acceptor. The OSCs based on PTQ10:IDIC-2F with PDINO–G CIM demonstrated the best power conversion efficiency (PCE) of 13.01%, which was significantly enhanced in comparison with that of the devices without graphene modification on the PDINO CIM (12.23%). The universality of the high performance PDINO–G CIM was verified in two other photovoltaic systems based on PTQ10:IDIC and PM6:Y6. Especially, the single junction bulk heterojunction OSCs based on PM6:Y6 with PDINO–G CIM displayed a high PCE of 16.52% (average PCE of 16.3 ± 0.2%). The results indicate that the n-doped PDINO–G is an excellent CIM for OSCs. Furthermore, this PDINO-doped graphene can be applied in other optoelectronic devices such as tandem OSCs, organic light-emitting diodes, and high-performance perovskite solar cells as a cathode interfacial material considering its advantages of solution processability, low work function and high conductivity.

An alcohol soluble hybrid organic–inorganic three-dimensional material 1,3,5,7,9,11,13,15-(9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-octavinylpentacyclo-octasiloxane (POSS-FN) has been synthesized and assessed as a cathode interlayer within organic solar cells consisting of a PBDT-BT:PC61BM bulk heterojunction. For comparison, we also studied another two linear interfacial materials: a typical conjugated polymer poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl)-fluorene] (PFN) and an insulating polymer poly(4-N,N-dimethylamino-styene) (PStN) in the same system. The hybrid interlayer caused a significant improvement to the device power conversion efficiency by 32%, comparable to the other two interlayers. We found that there are two kinds of interfacial dipoles formation: one weak but unfavourable between the interlayer and the active layer, and the other larger, favourable and significant between the interlayer and the cathode. This latter factor maximized the built-in electric field across the interlayer-modified devices, which provides one of the major reasons for the improved performance. The thermodynamics study revealed that the driving force for the dipole formation could be ascribed to the amino groups.

An amine-based, alcohol-soluble fullerene [6,6]-phenyl-C61-butyric acid 2-((2-(dimethylamino)ethyl)(methyl)amino)-ethyl ester (PCBDAN) with 4-fold electron mobility of 6,6-phenyl-C61-butyric acid methyl ester (PCBM) is applied successfully as an acceptor and cathode interfacial material in polymer solar cells ITO/P3HT:PCBDAN/MoO3/Ag, where indium tin oxide (ITO) alone is used as the cathode and poly(3-hexylthiophene) (P3HT) is used as a donor. The X-ray photoelectron spectroscopy (XPS) depth profile confirming a favorable vertical phase separation is formed where P3HT is rich at the air/active blend interface and PCBDAN is rich at the buried interface with ITO and, thus, reduces the work function of ITO for use as the cathode. A moderate power conversion efficiency (PCE) of 3.1% is achieved. The slightly low PCE could be due to unoptimized morphology and low structure ordering of P3HT in the blends. However, this result demonstrates that the amine-based fullerene could be used as the acceptor and cathode ...

We present a strategy to fabricate polymer solar cells in inverted geometry by self-organization of alcohol soluble cathode interfacial materials in donor-acceptor bulk heterojunction blends. An amine-based fullerene [6,6]-phenyl-C61-butyric acid 2-((2-(dimethylamino)-ethyl)(methyl)amino)ethyl ester (PCBDAN) is used as an additive in poly(3-hexylthiophene) (P3HT) and 6,6-phenyl C61-butyric acid methyl ester (PCBM) blend to give a power conversion efficiency of 3.7% based on devices ITO/P3HT:PCBM:PCBDAN/MoO3/Ag where the ITO alone is used as the cathode. A vertical phase separation in favor of the inverted device architecture is formed: PCBDAN is rich on buried ITO surface reducing its work function, while P3HT is rich on air interface with the hole-collecting electrode. The driving force of the vertical phase separation is ascribed to the surface energy and its components of the blend compositions and the substrates. Similar results are also found with another typical alcohol soluble cathode interfacial materials, poly[(9,9-bis(3'-(N, N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN), implying that self-organization may be a general phenomenon in ternary blends. This self-organization procedure could eliminate the fabrication of printing thin film of interlayers or printing on such thin interlayers and would have potential application for roll-to-roll processing of polymer solar cells.

A series of self n-doped fullerene ammonium derivatives have been synthesized and confirmed with electron paramagnetic resonance and conductivity measurements. The existence of stable C60O2˙− anion radical in these materials resulted in intrinsically high conductivities between 1.05 × 10−2 and 1.98 × 10−2 S cm−1. Among fullerenes with different numbers of ammonium and counter anions, [6,6]-phenyl-C61-butyric acid 2-((2-(trimethylammonium)ethyl)-(dimethyl)ammonium)-ethyl ester diiodides (PCBDANI) showed the best solvent resistance, which was confirmed by the measurement of film thickness and corresponding UV-vis absorption before and after rinsing with dichlorobenzene. Most importantly, the inverted polymer solar cells with the structure of ITO/PCBDANI/P3HT:PCBM/MoO3/Ag retained reasonably high power conversion efficiency even at a thickness of 82 nm of the PCBDANI film as the cathode interlayer. Thus large-area devices via printing this interlayer or printing on this interlayer could become feasible.

An alcohol-soluble hyperbranched conjugated polymer HBPFN with a dimethylamino moiety is synthesized and used as a cathode interlayer. A PCE of 7.7% is obtained for PBDTTT-C-T/PC71 BM based solar cells. No obvious interfacial dipole is found at the interface between the active layer and HBPFN however, an interfacial dipole with the cathode could be one of the reasons for the enhanced performance.