Conducting polymers are promising candidates in the fields of energy, information, biology and so on, mainly owing to their excellent merits of simple synthesis, easy-processing, good film forming ability, as well as controllable physical and chemical properties. Among various conducting polymers, aqueous PEDOT:PSS is known for its high transmittance and high conductivity, and has been widely used in the fields of solar cells, supercapacitors, thermoelectric devices and so on. For broader application of PEDOT:PSS in the optoelectronic devices, more efforts are needed to tune its processing technique, conductivity, work function and optical properties to be compatible with particular devices. Recently, Prof. Yinhua Zhou’s group from Wuhan National Laboratory for Optoelectronics (WNLO) has made a series of progress on the property tuning of PEDOT:PSS films, and applied them as the top electrodes for both organic and perovskite single-junction solar cells and tandems, flexible polymer supercapacitors. More details are included as follows:
(1) Perovskite solar cells have been attracting great attention due to its easy processing and high efficiency in the past several years. However, perovskite film is very sensitive to moisture while PEDOT:PSS is often deposited from aqueous solution, thus limiting the application of PEDOT:PSS in the field of perovkite solar cells. To solve this problem, the PhD student Ms. Fangyuan Jiang from the Prof. Yinhua Zhou’s group employed a film transfer printing technique and deposited the PEDOT:PSS film on top of the perovskite film/the hole-collecting layer as the top electrode (Figure 1a). The transfer printing method is the aqueous PEDOT:PSS solution was firstly deposited onto a transfer medium (such as PDMS or even plastic wrap), then transfer laminated onto the perovskite substrate (with spiro-OMeTAD on top of perovskite film) as the top electrode. The new device structure and the fabrication strategy enable the production of the perovskite solar cell with vacuum-free processing that is potentially low-cost and compatible with large-area fabrication.
This work has been published in Optics Express, 2015, 23, A83-91.
Furthermore, based on the PEDOT:PSS films, the group designed a new charge recombination layer (CRL) composing of spiro-OMeTAD/PEDOT:PSS/PEI/PCBM:PEI. With this CRL, the first bottom-up solution-processible perovskite/perovskite tandem solar cell was successfully fabricated. This work has been published by the Journal of Materials Chemistry A, 2015, DOI: 10.1039/C5TA08744A.
Fig.1 (a) Schematic of the perovskite solar cell employing PEDOT:PSS as the top electrode; (b) Schematic of perovskite/perovskite tandem solar cell with newly-designed CRL composing of spiro-OMeTAD/PEDOT:PSS/PEI/PCBM:PEI.
(2) Conducting polymers are also starting to be used for supercapacitors, and thermalelectrics. It has been a challenge to fabricate highly conductive, micrometers-thick and uniform polymer films. Here, Prof. Yinhua Zhou’s group develop a novel scalable strategy to prepare highly conductive thick poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (HCT-PEDOT:PSS) films by dropping the PEDOT:PSS aqueous dispersion into dilute surfulric acid solution to form precipitates and further PEDOT:PSS paste. The HCT-PEDOT:PSS films with layered structure display a conductivity up to 1400 S/cm and a low sheet resistance down to 0.59 ohm/sq. Organic solar cells with laminated HCT-PEDOT:PSS exhibit comparable performance to the reference devices with vacuum-deposited Ag top electrodes. Solid-state flexible symmetric supercapacitors with the HCT-PEDOT:PSS films display a high volumetric energy density of 3.15 mWh cm^-3 at a very high power density of 16160 mW cm^-3 that outperforms previous reported solid-state supercapacitors based on PEDOT materials. This work has been published inAngewandte Chemie International Edition, DOI: 10.1002/ange.201509033 and selected as “hot paper”.
Fig.2 (a) Schematic illustrations for the fabrication procedure of the HCT-PEDOT:PSS film. (b) Picture of a fabricated HCT-PEDOT:PSS film and the cross-sectional SEM image of the film
These works were supported by the Recruitment Program of Global Youth Experts, the National Natural Science Foundation of China (grant number 21474035, 51403071), the Fundamental Research Funds for the Central Universities, HUST (grant number 2014YQ013), Postdoctoral Science Foundation of China (grant numbers 2014M562016 and 2015T80794).