Sixing Xiong

A two-terminal perovskite/perovskite tandem solar cell

Building a tandem structure is an effective strategy to enhance the photovoltaic performance of solar cells. In the realization of a two-terminal tandem device, the charge recombination layer (CRL) plays an essential role. In the current study, we demonstrate the first bottom-up solution-processed two-terminal perovskite/perovskite tandem solar cell via developing a novel CRL: spiro-OMeTAD/PEDOT:PSS/PEI/PCBM:PEI. This CRL is efficient to collect electrons and holes at its top and bottom surfaces, and robust enough to protect the bottom perovskite film during the top perovskite film deposition. Moreover, the CRL is prepared by orthogonal solvent processing at low temperature, which is compatible with the pre-deposited perovskite film underneath. The PEI/PCBM:PEI is specially developed for efficient electron collection in both single-junction and tandem perovskite solar cells. With the optimized CRL to bridge the two CH3NH3PbI3 perovskite subcells, the tandem solar cell yields an open-circuit voltage (VOC) of up to 1.89 V that is close to the sum of the two perovskite subcells.

Conductivity Enhancement of PEDOT:PSS Films via Phosphoric Acid Treatment for Flexible All-Plastic Solar Cells

UNLABELLED Highly conductive polymer films on plastic substrates are desirable for the application of flexible electronics. Here, we report the conductivity of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) ( PEDOT PSS) can be enhanced to 1460 S/cm via phosphoric acid (H3PO4) treatment. The conductivity enhancement is associated with the partial removal of PSS from the film. The H3PO4 treatment is compatible with plastic substrates, while sulfuric acid (H2SO4) can easily damage the plastic substrate. With the flexible electrode of poly(ether sulfone) (PES)/H3PO4-treated PEDOT PSS, we have demonstrated flexible all-plastic solar cells (PES/H3PO4-treated PEDOT PSS/PEI/P3HT:ICBA/EG-PEDOT:PSS). The cells exhibit an open-circuit voltage of 0.84 V, a fill factor of 0.60, and a power conversion efficiency of 3.3% under 100 mW/cm(2) white light illumination.

Metal electrode–free perovskite solar cells with transfer-laminated conducting polymer electrode

UNLABELLED We report perovskite solar cells with a new device structure that employ highly conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) ( PEDOT PSS) as the top electrode replacing commonly used metal electrodes. The PEDOT PSS top electrode is prepared from its aqueous solution through a transfer-lamination technique rather than direct spin-coating, which converts the CH(3)NH(3)PbI(3) into PbI(2). Perovskite solar cells with the structure of glass/FTO/c-TiO(2)/m-TiO(2)/CH(3)NH(3)PbI(3)/spiro-OMeTAD/PEDOT:PSS yield a maximum open-circuit voltage (V(OC)) of 1.02 V, and a maximum power conversion efficiency (PCE) of 11.29% under AM1.5 100 mW/cm(2) illumination. The whole device was fabricated in air without high-vacuum deposition which simplifies the processing and lowers the threshold of both scientific research and industrial production of perovskite solar cells.

Flexible all-solution-processed all-plastic multijunction solar cells for powering electronic devices

A low-cost, light-weight and flexible power supply is highly desirable for portable electronic devices. All-plastic solar cells in which all the layers are fabricated sequentially from organic synthetic inks could meet these requirements. Here, we report that fully solution-processed all-plastic multijunction solar cells can be easily fabricated layer by layer without the need for sophisticated patterning. The key for the high-yield fully solution-processed multijunction cells is the control and tuning of the conductivity of the charge-recombination layer of PEDOT:PSS/PEI. The all-plastic multijunction solar cells achieve a PCE of 6.1 ± 0.4% and a high open-circuit voltage of 5.37 V. These all-plastic multijunction solar cells are successfully used to drive liquid-crystal displays, full-color light-emitting diodes and for water splitting under different light illumination conditions.

Polyethylenimine Aqueous Solution: A Low-Cost and Environmentally Friendly Formulation to Produce Low-Work-Function Electrodes for Efficient Easy-to-Fabricate Organic Solar Cells

Polyethylenimine (PEI) has been widely used to produce low-work-function electrodes. Generally, PEI modification is prepared by spin coating from 2-methoxyethanol solution. In this work, we explore the method for PEI modification on indium tin oxide (ITO) by dipping the ITO sample into PEI aqueous solution for organic solar cells. The PEI prepared in this method could reduce the work function of ITO as effectively as PEI prepared by spin coating from 2-methoxyethanol solution. H2O as the processing solvent is more environmentally friendly and much cheaper compared to the 2-methoxyethanol solvent. The dipping method is also compatible with large-area samples. With low-work-function ITO treated by the dipping method, solar cells with a simple structure of glass/ITO/PEI(dipping)/P3HT:ICBA/PEDOT:PSS(vacuum-free processing) display a high open-circuit voltage of 0.86 ± 0.01, a high fill factor of 66 ± 2%, and power conversion efficiency of 4.4 ± 0.3% under 100 mW/cm(2) illumination.

Universal Strategy To Reduce Noise Current for Sensitive Organic Photodetectors

Low noise current is critical for achieving high-detectivity organic photodetectors. Inserting charge-blocking layers is an effective approach to suppress the reverse-biased dark current. However, in solution-processed organic photodetectors, the charge-transport material needs to be dissolved in solvents that do not dissolve the underneath light-absorbing layer, which is not always possible for all kinds of light-absorbing materials developed. Here, we introduce a universal strategy of transfer-printing a conjugated polymer, poly(3-hexylthiophene) (P3HT), as the electron-blocking layer to realize highly sensitive photodetectors. The transfer-printed P3HT layers substantially and universally reduced the reverse-biased dark current by about 3 orders of magnitude for various photodetectors with different active layers. These photodetectors can detect the light signal as weak as several picowatts per square centimeter, and the device detectivity is over 1012 Jones. The results suggest that the strategy of transfer-printing P3HT films as the electron-blocking layer is universal and effective for the fabrication of sensitive organic photodetectors.

Double-side responsive polymer near-infrared photodetectors with transfer-printed electrode

Low dark current is critical to realize high-performance near-infrared organic photodetectors (NIR-OPDs). In general, organic photodetectors (OPDs) are with vacuum-deposited metals as the top electrode. The deposition of such metal would inevitably form doping to the organic active layer and thus yield high dark current. Herein, we employ transfer-printed conducting polymer (tp-CP) as the top electrode instead of the vacuum-deposited metal electrode. The photodetector with tp-CP electrode exhibits over two orders of magnitude lower dark current density than the device with the vacuum-deposited metal electrode. The photodetector with tp-CP electrode displays a responsivity of 0.37 A W−1 at 850 nm and a low dark current density of 3.0 nA cm−2 at −0.2 V based on a near-infrared (NIR) active layer of PMDPP3T:PC61BM that absorbs photons up to 1000 nm. The detectivity of the NIR photodetector reaches as high as over 1013 Jones. Furthermore, the NIR photodetector is double-side responsive to incident light, either from the bottom or the top electrode, because the top tp-CP electrode shows similar transparency as the bottom indium-tin oxide electrode.

Indium tin oxide (ITO)-free, top-illuminated, flexible perovskite solar cells

Flexible and light-weight photovoltaics are desirable for applications that involve their integration with flexible electronics. In this study, we demonstrate efficient flexible perovskite solar cells with a novel device architecture (that is indium-tin-oxide (ITO) free and top-illuminated) using a low-temperature processed doped fullerene as the electron-transporting layer. Silver is used as the bottom electrode, and a transparent conducting polymer electrode is used as the top electrode for light illuminating through to the active layer. Stearyldimethylbenzylammonium chloride (SDBAC)-doped [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) was the electron-transporting layer wherein SDBAC could enhance the conductivity by three orders of magnitude and therefore enhance the solar cell performance. The ITO-free flexible perovskite solar cells display power conversion efficiency of 11.8% on a polyethersulfone substrate and can maintain 84% of the initial PCE after 1000 bending cycles at a bending radius of 6 mm.

Vacuum-free and metal electrode-free organic tandem solar cells

We report on vacuum-free and metal electrode–free organic tandem solar cells that use conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the top electrode. The PEDOT:PSS top electrode was deposited via film-transfer lamination that does not need high-vacuum processing. The fabricated tandem solar cells exhibit an open-circuit voltage of 1.62 V, which is nearly the sum of the VOC of individual subcells, a high fill factor up to 0.72, and averaged power conversion efficiency of 3.6% under 100 mW cm−2 AM 1.5 illumination. The effect of the patterning of charge recombination layer and electrodes on the device performance has also been discussed.

Flexible large-area organic tandem solar cells with high defect tolerance and device yield

The fabrication of thin layers of organic photoactive materials (typically ca. 100–200 nm thick) over large area is needed for the commercial realization of organic solar cells. This is challenging because defects on these thin layers can cause high leakage currents which lead to poor device performance and, ultimately, to poor device yield. Here, we report that organic solar cells with a tandem structure can display an increased tolerance to defects and are found less susceptible to parasitic area scaling-up effects compared to single-junction solar cells. We demonstrate 10.5 cm2 flexible tandem solar cells with a power conversion efficiency of 6.5% with a fabrication yield of over 90% in a laboratory environment. The high fabrication yield and good performance displayed by tandem organic solar cells suggest that despite their increased complexity, they could provide a viable path towards the commercial realization of efficient large-area organic solar cells.