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Energy level alignment at C<sub>60</sub>/DTDCTB/PEDOT:PSS interfaces in organic photovoltaics
Yoo, Jisu,Jung, Kwanwook,Jeong, Junkyeong,Hyun, Gyeongho,Lee, Hyunbok,Yi, Yeonjin Elsevier BV * North-Holland 2017 Applied Surface Science Vol.402 No.-
<P><B>Abstract</B></P> <P>The electronic structure of a narrow band gap small molecule ditolylaminothienyl–benzothiadiazole–dicyanovinylene (DTDCTB), possessing a donor-acceptor-acceptor configuration, was investigated with regard to its application as an efficient donor material in organic photovoltaics (OPVs). The interfacial orbital alignment of C<SUB>60</SUB>/DTDCTB/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was determined using in situ ultraviolet photoelectron and inverse photoelectron spectroscopic methods. The ionization energy and electron affinity values of DTDCTB were measured to be 5.27eV and 3.65eV, respectively, and thus a very small transport gap of 1.62eV was evaluated. Large band bending of DTDCTB on PEDOT:PSS was observed, resulting in a low hole extraction barrier. Additionally, the photovoltaic gap between the highest occupied molecular orbital level of the DTDCTB donor and the lowest unoccupied molecular orbital level of the C<SUB>60</SUB> acceptor was estimated to be 1.30eV, which is known to be the theoretical maximum open-circuit voltage in OPVs employing the C<SUB>60</SUB>/DTDCTB active layer. The unique electronic structures of DTDCTB contributed toward the recently reported excellent power conversion efficiencies of OPVs containing a DTDCTB donor material.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The interfacial energy level alignment of C<SUB>60</SUB>/DTDCTB/PEDOT:PSS was determined via in situ UPS and IPES measurements. </LI> <LI> A large photovoltaic gap of 1.30eV was evaluated between the DTDCTB donor and C<SUB>60</SUB> acceptor. </LI> <LI> A low hole extraction barrier of 0.42eV from DTDCTB to PEDOT:PSS was evaluated. </LI> <LI> The excellent electronic properties of DTDCTB with a narrow band gap were the source of its high OPV power conversion efficiencies. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Electronic Structures of Nucleosides as Promising Functional Materials for Electronic Devices
Youn, Yungsik,Jung, Kwanwook,Lee, Younjoo,Park, Soohyung,Lee, Hyunbok,Yi, Yeonjin American Chemical Society 2017 The Journal of Physical Chemistry Part C Vol.121 No.23
<P>The energy level alignments of nucleosides fabricated between conventional Al and indium tin oxide (ITO) electrodes by means of a vacuum electrospray deposition technique were investigated using in situ ultraviolet and X-ray photoelectron spectroscopy measurements. The electronic structures of four nucleosides-deoxyguanosine, deoxyadenosine, deoxycytidine, and deoxythymidine-were determined, and their interactions with Al and ITO were analyzed. When in contact with ITO, each nucleoside showed an interface dipole that reduced the work function. On the other hand, when Al was deposited on the nucleoside layers, strong chemical interactions were observed due to electron transfer from Al to the nucleosides. Compared to their nucleobase counterparts, nucleosides commonly had lower ionization energies (IEs) and electron affinities (EAs). The origin of this difference in electronic structure was analyzed with density functional theory calculations. The sugar moieties in the nucleosides were found to induce electron-donating effects on the base moiety and led to reductions in IE and EA.</P>