Yong-Jin Noh

Efficient work-function engineering of solution-processed MoS2 thin-films for novel hole and electron transport layers leading to high-performance polymer solar cells

The work-function of MoS2 interfacial layers can be efficiently modulated by p- and n-doping treatments. As a result, the PCE of devices with a p-doped MoS2-based HTL is increased from ∼2.8 to ∼3.4%. Particularly, after n-doping the PCE was dramatically increased due to the change in work-function compared with un-doped MoS2 thin-films.

Sulfonic acid-functionalized, reduced graphene oxide as an advanced interfacial material leading to donor polymer-independent high-performance polymer solar cells

A r-GO with sulfonic acid groups (sr-GO) was newly developed and it showed dramatically concentrated aqueous dispersions with high film conductivity. With the aid of sulfonic acid groups, good compatibility with various HOMO materials was achieved, resulting in PCEs over 7% for sr-GO-based cells with superior device stability to PEDOT:PSS-based devices.

Efficient organic solar cells with solution-processed carbon nanosheets as transparent electrodes

We demonstrate that solution-processed carbon nanosheet (CNS) films can efficiently serve as transparent electrodes for organic solar cells (OSCs). The CNS was obtained by spin-coating of polyacrylonitrile (PAN) dissolved in dimethylformamide on quartz substrates, followed by stabilization and carbonization processes to convert polymer into CNS. The thickness of the newly developed CNS films was easily controlled by varying the PAN solution concentration. The polymer-converted CNS films were intensively examined for the feasibility of the use as transparent anodes in solar cells. This approach could be highly desirable for all-solution-processed or printed OSCs.

Efficient PEDOT:PSS-Free Polymer Solar Cells with an Easily Accessible Polyacrylonitrile Polymer Material as a Novel Solution-Processable Anode Interfacial Layer.

UNLABELLEDnWe demonstrate that an easily accessible polyacrylonitrile (PAN) polymer can efficiently function as a novel solution-processable anode interfacial layer (AIL) to boost the device performances of polymer:fullerene-based solar cells (PSCs). The PAN thin film was simply prepared with spin-coating of a cost-efficient PAN solution dissolved in dimethylformamide on indium tin oxide (ITO), and the thin polymeric interlayer on PSC parameters and stability were systemically investigated. As a result, the cell efficiency of the PSC with PAN was remarkably enhanced compared to the device using bare ITO. Furthermore, with PAN, we finally achieved an excellent power conversion efficiency (PCE) of 6.7% and a very high PSC stability in PTB7:PC71BM systems, which constitute a highly comparable PCE and superior device lifetime relative to those of conventional PSCs with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (nnnPEDOTnPSS). These results demonstrate that the inexpensive solution-processed PAN polymer can be an attractivennnPEDOTnPSS alternative and is more powerful for achieving better cell performances and lower cost PSC production.

Efficient polymer solar cells with a solution-processed gold chloride as an anode interfacial modifier

The use of a solution-processed gold chloride (AuCl3) as an anode interfacial modifier was investigated for high-performance polymer solar cells (PSCs). Kelvin probe, 4-point probe, and X-ray photoelectron spectroscopy studies demonstrated that AuCl3 increases the indium-tin-oxide (ITO) work-function and decreases the ITO sheet resistance, because of Au nanoparticle formation and Cl adsorption by the AuCl3 treatment to induce a p-doping effect, thereby improving the built-in potential and interface resistance. As a result, the introduction of AuCl3 by simple solution processing remarkably improved cell-performances, indicating that AuCl3 is an efficient anode interfacial modifier for enhancing PSC-performance.

Metal chloride-treated graphene oxide to produce high-performance polymer solar cells

We introduce a simple but effective graphene oxide (GO) modification with metal chloride treatments to produce high-performance polymer solar cells (PSCs). The role of various metal chlorides on GO and their effects on device performances of PSCs was investigated. X-ray photoelectron spectroscopy, ultraviolet photoemission spectroscopy, and current-voltage measurement studies demonstrated that metal chloride can induce a p-doping effect and increase the GO work-function, thus resulting in an improved built-in potential and interfacial resistance in PSCs. The resultant PSCs with metal chloride exhibited improved device efficiency than those with the neat GO. Furthermore, with the metal chloride-doped GO, we finally achieved an excellent PSC-efficiency of 6.58% and a very desirable device stability, which constitute a highly similar efficiency but much better PSC life-time to conventional device with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). This study could be a valuable way to produce various PEDOT:PSS alternatives and beneficial for producing high-performance and cost-efficient polymeric devices.

Roll-to-roll sputtered Si-doped In2O3/Ag/Si-doped In2O3 multilayer as flexible and transparent anodes for flexible organic solar cells

Amorphous Si-doped In2O3 (a-ISO), crystalline Ag, and a-ISO layers were sputtered onto a flexible polyethylene terephthalate substrate by using a lab-scale roll-to-roll (RTR) sputtering system. The resulting a-ISO/Ag/a-ISO multilayer was studied to optimize their characteristics for use as flexible and transparent anodes in flexible organic solar cells (FOSCs). To optimize the electrical and optical properties of the a-ISO/Ag/a-ISO multilayer, the thicknesses of each a-ISO and Ag layer were varied by controlling the DC power applied on ISO and Ag targets during the RTR sputtering process. Compared to the top and bottom a-ISO layer, controlling the thickness of the Ag layer is more effective for realizing a low sheet resistance and high transmittance a-ISO/Ag/a-ISO multilayer. At optimized thicknesses of a-ISO (30u2009nm) and Ag (10u2009nm), a symmetric a-ISO/Ag/a-ISO multilayer showed a sheet resistance of 5.256 Ω/sq and a high optical transmittance of 83.9%. Various bending test results showed that the high fail...

Ag-Pd-Cu alloy inserted transparent indium tin oxide electrodes for organic solar cells

The authors report on the characteristics of Ag-Pd-Cu (APC) alloy-inserted indium tin oxide (ITO) films sputtered on a glass substrate at room temperature for application as transparent anodes in organic solar cells (OSCs). The effect of the APC interlayer thickness on the electrical, optical, structural, and morphological properties of the ITO/APC/ITO multilayer were investigated and compared to those of ITO/Ag/ITO multilayer electrodes. At the optimized APC thickness of 8u2009nm, the ITO/APC/ITO multilayer exhibited a resistivity of 8.55u2009×u200910−5 Ω cm, an optical transmittance of 82.63%, and a figure-of-merit value of 13.54u2009×u200910−3 Ω−1, comparable to those of the ITO/Ag/ITO multilayer. Unlike the ITO/Ag/ITO multilayer, agglomeration of the metal interlayer was effectively relieved with APC interlayer due to existence of Pd and Cu elements in the thin region of the APC interlayer. The OSCs fabricated on the ITO/APC/ITO multilayer showed higher power conversion efficiency than that of OSCs prepared on the ITO/Ag...

ZnO films using a precursor solution irradiated with an electron beam as the cathode interfacial layer in inverted polymer solar cells

We demonstrate the possibility of irradiating sol–gel ZnO with an electron beam (EB-ZnO) to modify sol–gel ZnO, and EB-ZnO is explored as a cathode interfacial layer for inverted polymer solar cells. We investigate the effect of EB-ZnO on the surface, optical and electric properties of sol–gel ZnO films through morphology, chemical composition, optical band gap shift, various defect excitations (photoluminescence) and work function measurement. Oxygen vacancies and the formation of nitrogen on the surface of EB-ZnO films contribute to the formation of n-type degenerated EB-ZnO films. The electric properties of EB-ZnO strongly depend on the adsorbed dose, and EB-ZnO with a suitable dose of 100 kGy improved the power conversion efficiency of inverted polymer solar cells based on PTB7-Th: PC71BM from 8.05% for non-treated sol–gel ZnO to 9.36% for EB-ZnO with an enhanced fill factor.

Tin doped indium oxide anodes with artificially controlled nano-scale roughness using segregated Ag nanoparticles for organic solar cells

Nano-scale surface roughness in transparent ITO films was artificially formed by sputtering a mixed Ag and ITO layer and wet etching of segregated Ag nanoparticles from the surface of the ITO film. Effective removal of self-segregated Ag particles from the grain boundaries and surface of the crystalline ITO film led to a change in only the nano-scale surface morphology of ITO film without changes in the sheet resistance and optical transmittance. A nano-scale rough surface of the ITO film led to an increase in contact area between the hole transport layer and the ITO anode, and eventually increased the hole extraction efficiency in the organic solar cells (OSCs). The heterojunction OSCs fabricated on the ITO anode with a nano-scale surface roughness exhibited a higher power conversion efficiency of 3.320%, than that (2.938%) of OSCs made with the reference ITO/glass. The results here introduce a new method to improve the performance of OSCs by simply modifying the surface morphology of the ITO anodes.