Yulei Wu

High performance polymer solar cells with a polar fullerene derivative as the cathode buffer layer

A highly efficient polymer solar cell was fabricated using a polar fullerene derivative C60 pyrrolidine tris-acid (CPTA) as the cathode buffer layer. By introducing CPTA, the Voc, Jsc and FF were all much enhanced simultaneously. The power conversion efficiency (PCE) was significantly improved to 7.92%, which outperformed the device using Ca/Al as the cathode in our experiment.

Side-Chain Engineering of Benzodithiophene-Fluorinated Quinoxaline Low-Band-Gap Co-polymers for High-Performance Polymer Solar Cells

A new series of donor-acceptor co-polymers based on benzodithiophene and quinoxaline with various side chains have been developed for polymer solar cells. The effect of the degree of branching and dimensionality of the side chains were systematically investigated on the thermal stability, optical absorption, energy levels, molecular packing, and photovoltaic performance of the resulting co-polymers. The results indicated that the linear and 2D conjugated side chains improved the thermal stabilities and optical absorptions. The introduction of alkylthienyl side chains could efficiently lower the energy levels compared with the alkoxyl-substituted analogues, and the branched alkoxyl side chains could deepen the HOMO levels relative to the linear alkoxyl chains. The branched alkoxyl groups induced better lamellar-like ordering, but poorer face-to-face packing behavior. The 2D conjugated side chains had a negative influence on the crystalline properties of the co-polymers. The performance of the devices indicated that the branched alkoxyl side chains improved the Voc, but decreased the Jsc and fill factor (FF). However, the 2D conjugated side chains would increase the Voc, Jsc, and FF simultaneously. For the first time, our work provides insight into molecular design strategies through side-chain engineering to achieve efficient polymer solar cells by considering both the degree of branching and dimensionality.

Solution-Processed Hybrid Cathode Interlayer for Inverted Organic Solar Cells

A novel hybrid material CdS/2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (CdS·BCP) was prepared from the decomposition of its organic soluble precursor complex Cd(S2COEt)2·(BCP) by low-temperature treatment. CdS·BCP, which integrated the favorable properties of solvent durability, and high electron mobility of CdS as well as the good hole blocking property of BCP, was designed and developed as the interface modification material to improve electron collection in bulk heterojunction organic solar cells (OSCs). The inverted OSCs with CdS·BCP as buffer layer on ITO showed improved efficiency compared with the pure CdS or BCP. Devices with CdS·BCP as interlayer exhibited excellent stability, only 14.19% decay of power conversion efficiencies (PCEs) was observed (from 7.47% to 6.41%) after stored in glovebox for 3264 h (136 days). Our results demonstrate promising potentials of hybrid materials as the interface modification layers in OSCs, and provide new insights for the development of new interface modification materials in the future.

Solution-Processed MoSx as an Efficient Anode Buffer Layer in Organic Solar Cells

We reported a facile solution-processed method to fabricate a MoSx anode buffer layer through thermal decomposition of (NH4)2MoS4. Organic solar cells (OSCs) based on in situ growth MoSx as the anode buffer layer showed impressive improvements, and the power conversion efficiency was higher than that of conventional PEDOT:PSS-based device. The MoSx films obtained at different temperatures and the corresponding device performance were systematically studied. The results indicated that both MoS3 and MoS2 were beneficial to the device performance. MoS3 could result in higher Voc, while MoS2 could lead to higher Jsc. Our results proved that, apart from MoO3, molybdenum sulfides and Mo(4+) were also promising candidates for the anode buffer materials in OSCs.

Improving Efficiency by Hybrid TiO2 Nanorods with 1,10-Phenanthroline as A Cathode Buffer Layer for Inverted Organic Solar Cells

We reported a significant improvement in the efficiency of organic solar cells by introducing hybrid TiO2:1,10-phenanthroline as a cathode buffer layer. The devices based on polymer thieno[3,4-b]thiophene/benzodithiophene:[6,6]-phenyl C71-butyric acid methyl ester (PTB7:PC71BM) with hybrid buffer layer exhibited an average power conversion efficiency (PCE) as high as 8.02%, accounting for 20.8% enhancement compared with the TiO2 based devices. The cathode modification function of this hybrid material could also be extended to the poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) system. We anticipate that this study will stimulate further research on hybrid materials to achieve more efficient charge collection and device performance.

Critical role of the external bias in improving the performance of polymer solar cells with a small molecule electrolyte interlayer

A small-molecule electrolyte based on the popular ethylene diamine tetraacetic acid (EDTA-N) is introduced as an efficient cathode interlayer in inverted polymer solar cells, helping to deliver power conversion efficiency over 9%. The strong dependence of device performance on the external bias suggests that the ion motion plays a critical role in improving the performance of devices with electrolyte interlayers.

High-Performance Polymer Solar Cells with Zinc Sulfide-Phenanthroline Derivatives as the Hybrid Cathode Interlayers.

Environmentally benign hybrid interlayers are prepared by modifying the zinc sulfide (ZnS) with phenanthroline/derivatives and utilized in inverted polymer solar cells (PSCs). Performances of the inverted PSCs are improved enormously by incorporating these hybrid interlayers, as which can effectively improve the energy level alignment, electron mobility, surface morphology, and interfacial contact. Greatly improved power conversion efficiencies (PCEs) of 7.79%, 8.00%, 7.47%, and 7.56% are achieved with these hybrid interlayers ZnS-BCP, ZnS-Bphen, ZnS-Mphen, and ZnS-Phen, respectively, compared to the PCE of 2.99% of the reference ZnS-based device, based on PTB7:PC71BM active layer. Our results demonstrate that hybrid interfacial materials comprising inorganic and organic semiconductor possess promising potential to improve the performance of organic electronic devices, and set an example to develop this novel class of interfacial materials for electronic devices.

CdS–phenanthroline derivative hybrid cathode interlayers for high performance inverted organic solar cells

Phenanthroline based organic semiconductors (BCP, Bphen, Mphen, and Phen) are used to hybrid with CdS as cathode interlayers in inverted organic solar cells (OSCs). We observed that selecting the polar solvent and hydrophobic interlayers with a diphenyl group could improve the performance of the organic photovoltaic devices. The modification to CdS can effectively improve its electron mobility, film morphology, interfacial contact, and energy level alignment, which finally leads to a significant enhancement of device performance. Through incorporating the CdS–P hybrids (CdS–BCP, CdS–Bphen, CdS–Mphen, and CdS–Phen) as cathode buffer layers, the device PCE (PTB7 : PC71BM as the active layer) is greatly improved from 3.09% to 8.36, 7.84, 6.69, and 6.57%, respectively, compared with devices fabricated on the pristine CdS interlayer. These results indicate that the common inorganic semiconductor like CdS can be modified using some organic semiconductors to produce general applicable electron transport layers applied in OSCs. Our work puts forward new insights for the development of new interface modification materials and fabrication of high efficiency devices.