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Takuma Ohashi, Masaki Ishii, [Jun Takeya](https://orcid.org/0000-0002-7003-1350), [Katsuhiko Ariga](https://orcid.org/0000-0002-2445-2955), [Yu Yamashita](https://orcid.org/0000-0001-7966-3197)

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[Biochemical Pathways for n‐Type Doping: An Electron Transfer Relay from Saccharide to Organic Semiconductors](https://mdr.nims.go.jp/datasets/ffe93a7f-49b0-4af3-af52-7159f2b5f9f0)

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Biochemical Pathways for n‐Type Doping: An Electron Transfer Relay from Saccharide to Organic SemiconductorsRESEARCH ARTICLEwww.small-journal.comBiochemical Pathways for n-Type Doping: An ElectronTransfer Relay from Saccharide to Organic SemiconductorsTakuma Ohashi, Masaki Ishii,* Jun Takeya, Katsuhiko Ariga, and Yu Yamashita*Solution processing of organic semiconductors provides a facile way tofabricate electrically doped thin films, which opens opportunities foradvancing printed electronics. However, this approach is limited due to theinstability of dopants and doped organic semiconductors, particularly forn-type ones. In this study, n-type doping of an organic semiconductingpolymer is achieved using aqueous doping solutions in air, a condition underwhich n-type chemical doping had not previously been demonstrated.Polymeric semiconductor thin films are immersed in aqueous dopingsolutions, which contained the saccharide fructose, redox bio-mediator flavinnucleotide (FMN), and bulky molecular cations. In this process, electrons aretransferred from fructose to FMN and then from FMN to organicsemiconductor thin films. The introduced electrons are compensated by theincorporation of bulky molecular cations into the thin films. Successful n-typedoping is confirmed by absorption, conductivity, and photoelectronspectroscopy measurements. The density of states of the polymer is filled upto −3.8 eV versus vacuum, beyond the conventionally anticipated limit ofambient stability. This breakthrough is rooted in the combined effects ofsolution pH, mediator-assisted use of fructose, and choice of dopant cation.In addition, n-type doping using biomolecules may shed light on newconnections between electronic materials and biomolecules for energystorage, transfer, and conversion.T. Ohashi, M. Ishii, J. Takeya, K. Ariga, Y. YamashitaResearch Center for Materials Nanoarchitectonics (MANA)National Institute for Materials Science (NIMS)1-1 Namiki, Tsukuba, Ibaraki 305-0044, JapanE-mail: 7221701@alumni.tus.ac.jp; yamashita.yu@nims.go.jpT.Ohashi,M. Ishii, K. ArigaGraduate School of Science andTechnologyTokyoUniversity of Science2641Yamazaki,Noda, Chiba 278-8510, JapanJ. Takeya, K. Ariga, Y. YamashitaDepartment of AdvancedMaterials ScienceGraduate School of Frontier SciencesTheUniversity of Tokyo5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, JapanThe ORCID identification number(s) for the author(s) of this articlecan be found under https://doi.org/10.1002/smll.202509278© 2025 The Author(s). Small published by Wiley-VCH GmbH. This is anopen access article under the terms of the Creative CommonsAttribution-NonCommercial License, which permits use, distribution andreproduction in any medium, provided the original work is properly citedand is not used for commercial purposes.DOI: 10.1002/smll.2025092781. IntroductionOrganic semiconductors feature solutionprocessability and electronic propertiesthat are tunable by molecular design,[1,2]making them candidate materials forprinted electronics. Recently, chemicaldoping of organic semiconductors hasbeen employed to improve the perfor-mances of photovoltaic cells,[3,4] thermo-electric generators,[5–8] transistors,[9–12]and diodes.[13,14] The doping levels oforganic semiconductors reach 1021 cm−3for both p-type and n-type,[15–19] whichhighlights their advantages over othersolution-processed semiconductors in-cluding oxides and halide perovskites.[20]Ion-exchange doping[15] has enabled theincorporation of stable dopant ions, signif-icantly improving both doping efficiencyand environmental stability. Recently,p-type chemical doping of organic semi-conductors was demonstrated usingaqueous solutions in air, where the use ofproton-coupled electron transfer (PCET)reactions offered substantial improvementsin both scalability and process control.[21]Together with its n-type counterpart—aqueous solution-based doping in air—thisadvancement marks a promising step toward the next paradigmin solution-processed organic semiconductors.To achieve reliable chemical doping, it is critical to suppressundesirable redox reactions with water and/or oxygen. For am-bient p-type doping, the reactivity of water is suppressed un-der low-pH conditions,[21] highlighting the advantage of us-ing pH-controlled aqueous doping solutions. For n-type dop-ing, in addition to the possible reactions with water, reactionswith oxygen in air must be addressed. Efficient n-type dop-ing requires that the ionization potential (IP) of the reducingagent be close to or smaller than the electron affinity (EA) ofthe semiconductor.[22] Given that typical electron-transportingorganic semiconductors have EAs around 4.0 eV, strong re-ducing agents are needed—agents that are generally suscep-tible to oxidation by oxygen under ambient conditions.[13] Al-though semiconductors with EA larger than 4.0 eV have beendeveloped,[23,24] materials with relatively small EAs remain im-portant for key applications such as photovoltaic cells, light-emitting diodes, and electron injection layers. To achieve strongand stable n-type chemical doping, various material and processstrategies have been investigated, including dimeric dopants,[25]Small 2025, 21, e09278 © 2025 The Author(s). Small published by Wiley-VCH GmbHe09278 (1 of 7)http://www.small-journal.commailto:7221701@alumni.tus.ac.jpmailto:yamashita.yu@nims.go.jphttps://doi.org/10.1002/smll.202509278http://creativecommons.org/licenses/by-nc/4.0/http://creativecommons.org/licenses/by-nc/4.0/http://crossmark.crossref.org/dialog/?doi=10.1002%2Fsmll.202509278&domain=pdf&date_stamp=2025-10-30www.advancedsciencenews.com www.small-journal.comFigure 1. N-type chemical doping under ambient conditions. a) Schematic illustrations of the model of the chemical doping process b) The chemicalstructures of the employed materials together with schematic illustrations of their possible redox reactions. c,d) UV–Vis spectra of the pristine andtreated PNDI(2HD)T thin films. The compounds dissolved in the treatment solutions are denoted as legends. For the red plot, fructose, FMN, anddMesIM-Cl were dissolved in an aqueous pH buffer containing 9vol% acetonitrile.catalytic doping,[26] and ion-exchange doping.[17,18] However,to the best of our knowledge, efficient n-type chemical dop-ing of organic semiconductors in air has yet to be demon-strated.While most strongly reducing agents are unstable in air, somebiomolecules simultaneously show reducing power and stabil-ity. One such example is fructose, a common saccharide foundin food. The ambient stability of fructose is due to its slow re-dox kinetics, where only the enediol form of fructose, which ispresent at a ratio of 0.4%, contributes to the redox reactions.[27]However, such slow redox kinetics are expected to hinder the effi-cient electron transfer to othermaterials, including organic semi-conductors. Thus, it is unclear whether such a stable biomolec-ular energy source can be employed for n-type doping, in whichelectrons from biomolecules must be transferred to and storedin semiconductors.In this study, we report n-type chemical doping of organicsemiconductors in air using aqueous solutions (Figure 1a). Toachieve a high reducing power and ambient stability of the re-ducing agents, we employed a combination of fructose and aredox mediator, flavin mononucleotide (FMN). Electron-transferreactions occurred from fructose to FMN and then from FMN tosemiconductors in our system, which resulted in efficient n-typedoping of the semiconductors. The electrons in the semiconduc-tors were compensated by bulky molecular cations, which wereselected to improve carrier transport properties and stability. UV–Vis, conductivity, and X-ray photoelectron spectroscopy (XPS)measurements supported our model shown in Figure 1a. Pho-toelectron yield spectroscopy (PYS) measurements suggested ef-fective filling of density of states up to −3.8 eV versus vacuumin our process. The n-type chemical doping demonstrated in airis a key enabler for the fabrication of advanced devices via solu-tion processing. In addition, electron transfer from fructose andFMN sheds light on a new connection between electronic mate-rials and biomolecules, in terms of energy storage, transfer, andconversion.Small 2025, 21, e09278 © 2025 The Author(s). Small published by Wiley-VCH GmbHe09278 (2 of 7) 16136829, 2025, 49, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202509278 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.com2. Results and Discussion2.1. n-Type Chemical Doping in Aqueous SolutionsOptical absorption measurements were performed to verifyambient n-type doping of organic semiconductor thin films.The chemical structures of the employed materials are shownin Figure 1b. We employed a polymer with naphthalene-1,4:5,8-bis(dicarboximide) (NDI) and thiophene backbone withbranched alkyl chains (PNDI(2HD)T). Polymer thin films werespin-coated on glass substrates and thermally annealed (see Ex-perimental Section for details). The doping solution was pre-pared by dissolving 1 M fructose, 10 mM FMN, and 10 mM1,3-dimesitylimidazolium chloride (dMesIM-Cl) in an alkalinebuffer solution and adding 9vol% acetonitrile to promotes dopantdiffusion. Chemical doping was performed by immersing thethin films in the doping solution in air at room tempera-ture. The results of the absorption measurements are shownin Figure 1c. The undoped pristine PNDI(2HD)T thin film ex-hibited the lowest energy excitation peak at ca. 610 nm. Af-ter immersion in the doping solution, this peak was bleached,and other peaks at ca. 500 and 785 nm appeared. This result isconsistent with successful n-type doping of polymeric semicon-ductors with NDI units forming polarons.[17,28,29] The conduc-tivity of the thin film increased from below 10−9 S cm−1 to 4× 10−4 S cm−1 by our process as shown later, which also sup-ports successful n-type doping. When fructose or FMN werenot dissolved in the doping solution, no spectral changes wereobserved (Figure 1d). These results show that the use of bothfructose and FMN is necessary to achieve n-type doping in ourprocess.Electrode potential measurements were performed to clarifythe roles of fructose and FMN (Figure 2a,b). Three solutions wereused in this experiment: a fructose solution (pH 10.6), FMN solu-tion (pH 10.9), and solution containing both fructose and FMN(pH 10.4). Measurements with the fructose solution showed apotential of −40 mV (versus Ag/AgCl). Although fructose is ex-pected to show a redox potential more negative than −700 mV atelevated temperatures and basic conditions[30] through the PCETreaction C6H12O6 + 2OH− → C6H12O7 +H2O + 2e−, its slow re-action rate at room temperature limits the attainable reducingpower. Consistently, the attainable doping level was found to de-pend on the solution pH, as discussed in Note S1 (SupportingInformation). The slow reaction rate is partly due to the smallproportion of the endiol form, which contributes to the reducingpower. When only FMN is dissolved, the electrode potential wasca. −20 mV versus Ag/AgCl. In contrast, when both fructose andFMN were dissolved, a shallow electrode potential of −490 mVversus Ag/AgCl was observed. This phenomenon is explained bythe redox mediator model, where FMN accepts electrons fromfructose and then donates electrons to the target electrode. Thus,while the reaction rate was too low for a direct redox reaction be-tween the electrode and fructose, FMN accelerated the redox re-actions by serving as a redox mediator. Details of electron trans-fer kinetics is discussed in Note S2 (Supporting Information).In addition, the solution with both fructose and FMN showeda shallow electrode potential at least for a few hours, demonstrat-ing balanced reducing power and stability in air. Combining theevaluation of PNDI(2HD)T energy level (Note S3, Supporting In-Figure 2. Roles of fructose and FMN. a) A schematic illustration of theelectrode potential measurements in aqueous pH-buffer solutions. b) Theresults of electrode potential measurements. The compounds dissolvedin solutions are denoted as legends. c) The energy diagram of our dopingprocess. d) The change in amount of dissolved oxygen in the pH-buffersolutions by time. The dissolved compounds are denoted as legends.formation), the energy diagram for the electron transfer relay isshown in Figure 2c.During the doping process, oxygen in the aqueous doping so-lution is eliminated by redox reactions, which is supported byan evaluation of the concentration of dissolved oxygen (DO). DOwasmeasured using a DOmeter equipped with amembrane thatselectively transports oxygen among redox-active materials. Notethat most of the doping reaction is completed within one hour,based on the UV–Vis measurements shown in Note S4 (Support-ing Information). Figure 2d shows the DO values measured inpH-buffer solutions containing fructose, FMN, or both. DO de-creased slowly in the solution containing fructose, which is con-sistent with the slow redox kinetics of fructose. In contrast, thecombination of FMN and fructose resulted in a sharp decrease inDO, with FMN serving as a redox mediator to accelerate the re-dox reaction rate. Thus, owing to the low solubility of oxygen inaqueous solutions and redox reactions with fructose and FMN,oxygen is present in our doping solution at very low concentra-tions and does not affect the doping efficiency.Based on the above results, the effects of reactions with waterand/or oxygen are suppressed in our doping method. Comparedwith the observed electrode potential of−490mV versus Ag/AgClin our system, the reduction potential of water is much morecathodic (ca. −790 mV versus Ag/AgCl[31]) at pH 10 and roomtemperature, where redox reactions with water may not give con-siderable effects. Note that the use of bulky hydrophobic ion isimportant for achieving doping at such a moderate potential.[21]Small 2025, 21, e09278 © 2025 The Author(s). Small published by Wiley-VCH GmbHe09278 (3 of 7) 16136829, 2025, 49, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202509278 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comFigure 3. XPS spectra of doped thin films. a) XPS survey spectra of the pristine and doped PNDI(2HD)T thin films. The cations of the salts employedare denoted as legends for doped thin films. The peaks marked with asterisks are assigned to the Si atoms that can originate from the substrate. XPSnarrow spectra of the pristine and doped PNDI(2HD)T thin films for b) C 1s, c) N 1s, d) O 1s, e) S 2p, and f) P 2p regions. The cations of the saltsemployed are denoted as legends for doped thin films.Although oxygen can consume dopant materials, this does notlimit the attainable doping levels during the process because ofthe low solubility of oxygen in water. Indeed, the solution withfructose and FMN showed negligible DO. Thus, the combined ef-fects of solution pH,mediator-assisted use of fructose, and choiceof dopant cation contributed to the achievement of ambient n-type chemical doping.2.2. Identification of Introduced Molecular CationsThe dopant cations incorporated in the thin films were identifiedby X-ray photoelectron spectroscopy (XPS). In this experiment,doping solutions were prepared by adding salts of dMesIM-Cl orbis(triphenylphosphoranylidene)ammonium chloride (TPPA-Cl)to pH buffer solutions containing fructose and FMN. Figure 3ashows the XPS survey spectra of the PNDI(2HD)T thin filmsbefore and after the doping process. The pristine thin film ex-hibited peaks for carbon, nitrogen, oxygen, and sulfur atoms,which is consistent with themolecular structure of PNDI(2HD)T.When TPPA-Cl was dissolved in the doping solution, P 2sand P 2p peaks were observed, suggesting the successful in-troduction of TPPA+ to the polymer thin film. The composi-tions of the doped thin films were further examined based ontheir narrow spectra (Figure 3b–f). When TPPA-Cl was used inthe doping solution, new peaks appeared in the P 2p and N1s regions. While undoped polymer showed an N 1s peak at400.6 eV, the additional peak was observed at 398.0 eV, whichis consistent with the binding energy expected for the nitrogenatom in TPPA+. Note that the lower binding energy for the ni-trogen atom in TPPA+ compared to that of NDI is supportedby our density functional theory (DFT) calculations (Note S5,Supporting Information), which indicate the negatively chargedcharacter of the nitrogen atom in TPPA+. These results supportthe incorporation of TPPA+ into the polymer thin film. WhendMesIM-Cl was used in the doping process, a new peak wasobserved at 402.0 eV, which is consistent with the binding en-ergy for positively charged nitrogen atoms in dMesIM+, indicat-ing the incorporation of dMesIM+ in the thin film. The den-sity of the incorporated cations was estimated by quantitativeanalysis of the XPS peaks. The ratios of the dopant/monomerunit were estimated to be 0.75 for dMesIM+doping and 0.48for TPPA+-doping, respectively, based on the N 1s peak areas(Note S6, Supporting Information). These results suggest theSmall 2025, 21, e09278 © 2025 The Author(s). Small published by Wiley-VCH GmbHe09278 (4 of 7) 16136829, 2025, 49, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202509278 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comFigure 4. Electronic properties of doped thin films. Results of a) UV–Vis-NIR absorption, b) conductivity, and PYS measurements of c) the pristineand d) doped PNDI(2HD)T thin films. The dopant cations employed aredenoted as legends. In PYSmeasurements, a deuterium (xenon) lampwasemployed for the pristine (doped) thin films.high doping levels of the polymer thin films achieved using ourmethod.The electronic properties of the dMesIM+-doped and TPPA+-doped thin films were further evaluated. In the UV–Vis–NIRspectra (Figure 4a), the dMesIM+-doped PNDI(2HD)T thin filmexhibited a near-infrared (NIR) absorption peak at approximately1480 nm, which can be attributed to polaron absorption. For theTPPA+-doped thin film, the NIR absorption peak shifted to alonger wavelength. Compared to the pristine thin film, the dopedPNDI(2HD)T thin films showed significantly higher conductivi-ties (Figure 4b). The TPPA+-doped film exhibited a conductivityof 2× 10−2 S cm−1, which was higher than that of the dMesIM+-doped film. These results suggest that polarons are more delocal-ized in the TPPA+-doped thin film than in the dMesIM+-dopedone, which may be attributed to differences in carrier concentra-tions, as discussed later. Photoelectron yield spectroscopy (PYS)measurements were performed to investigate changes in ioniza-tion potentials (IPs) upon doping (Figure 4c,d). In the PYS mea-surements, the wavelength of the incident UV light was sweptwhilemonitoring the photoelectron current and yield. The IPwasdetermined as the threshold energy at which the cube root of thephotoelectron yield begins to increase. The pristine PNDI(2HD)Tfilm showed an IP of 6.26 eV, consistent with the deep-lyinghighest occupied molecular orbital (HOMO) of an n-type organicsemiconductor. The doped thin films showed IPs of 3.73 eV forTPPA+ doping and 3.85 eV for dMesIM+ doping. These resultsare consistent with filling of the lowest unoccupied molecular or-bital (LUMO) density of states and support the UV–Vis–NIR andconductivity measurements.2.3. Stability of Doped State in Air at High TemperaturesThe effects of the dopant cations on the stability of the dopedthin films were evaluated based on the changes in conduc-tivity over time. Thin films were stored at room temperatureand 80% relative humidity, where dedoping by redox reactionswith H2O and O2 is anticipated,[13] considering the shallow IPsof the doped polymers. As a reference, a well-studied n-typedopant, 4-(1,3-Dimethyl-2,3-dihydro-1H-benzimidazol-2-yl)-N,N-dimethylaniline (N-DMBI-H), was also used. N-DMBI-H dopingwas conducted in anN2-purged glove box using an acetonitrile so-lution, where features of n-type doping were observed in UV–Vismeasurements (Note S7, Supporting Information). In this case,N-DMBI+ should be the dopant cation present in the polymerthin films.The use of dMesIM+ or TPPA+ in ourmethod resulted in supe-rior ambient stability of the doped thin films compared to the casewith N-DMBI-H doping (Figure 5a). While the initial conduc-tivity measured was similar for N-DMBI+- and dMesIM+dopedthin films, the N-DMBI+-doped film showed a faster decay in theconductivity, which is consistent with our previous study.[17] ThedMesIM+-doped thin film exhibited an initial increase in conduc-tivity for at least 4 h after air exposure. Changes inUV–Vis spectraare also shown in Note S8 (Supporting Information). This can beexplained by the reported increase in conductivity with a decreasein the doping levels at very high doping levels close to one elec-tron per monomer unit for NDI-based polymers.[17,32] This phe-nomenon also explains the differences in the UV–Vis–NIR spec-tra and conductivity measurements of TPPA+- and dMesIM+-doped thin films observed in Figure 3. For the tested three sam-ples, the lifetimes of the doped state were evaluated based on thetime required to observe a one-decade decrease in conductivityfrom the highest observed value (See Note S9, Supporting Infor-mation, for fitting). The lifetimes were 0.7 h, 1.7 h, and 28.7 h forN-DMBI+-, TPPA+, and dMesIM+-doped thin films, respectively.We also tested the thermal stability of the doped thin films inair (Figure 5b), which suggests the possibility of employing ourn-type doped materials in applications including thermoelectricgenerators. The dMesIM+-doped thin films were heated in air at100 °C, and the conductivity was measured repeatedly at roomtemperature. The dMesIM+-doped thin film exhibited a lifetimeof 5 h, which is shorter than that of the test at room tempera-ture. The results obtained at higher temperatures are presentedin Note S10 (Supporting Information). When a PMMA thin filmwas spin-coated onto the doped PNDI(2HD)T thin film as anSmall 2025, 21, e09278 © 2025 The Author(s). Small published by Wiley-VCH GmbHe09278 (5 of 7) 16136829, 2025, 49, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202509278 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comFigure 5. Stability of doped thin films in air. a) Changes in conductivity ofdoped PNDI(2HD)T thin films stored at room temperature and relativehumidity of 80%. The dopant cations are denoted as legends. b) Changesin conductivity of dMesIM+-doped PNDI(2HD)T thin films heated at 100°C in air or in a glove box. Samples with or without a PMMA encapsulationlayer were compared for the heating in air.encapsulation layer, the lifetime increased to 25 h.When the heat-ing process was conducted in a nitrogen-purged glove box andconductivity measurements were conducted in air, the thin filmdid not show a decrease in conductivity within 200 h, which sup-ports the thermal stability of our thin film. Overall, the resultssuggest that the degradation of doped thin films at 100 °C inair occurs owing to accelerated reactions with O2 and/or H2O,which is dramatically suppressed by the choice of dopant cationsand the use of facile thin-film encapsulation. The observed ther-mal stability in air was remarkable, considering the shallow IPof the doped thin films. Further exploration of dopant ions andpolymers using our method will lead to shallow IP yet stabledoped polymers, which is advantageous for applications such asthermoelectric generators and electron transport layers in pho-tovoltaic cells. Considering the effective energy levels of the em-ployed reducing agents, other types of polymers is expected to becompatible with ourmethod (as partly demonstrated inNote S11,Supporting Information).3. ConclusionIn this study, n-type chemical doping of a polymeric semicon-ductor was achieved using aqueous solutions in air, which wasconfirmed using absorption, XPS, conductivity, and PYS mea-surements. Fructose shows a slow redox reaction rate, which con-tributes to ambient stability, but limits its effective reducing ca-pability. The use of the FMN redox mediator balances the re-dox reaction rate to achieve n-type doping. The dMesIM+-dopedPNDI(2HD)T thin film exhibited a conductivity of > 10−3 S cm−1and prolonged lifetime in air at room and elevated temperatures.Owing to the thermal stability of the material, facile thin-film en-capsulation realized a lifetime of 25 h at 100 °C in air, whichis remarkable considering the shallow IP of around 3.8 eV forthe doped PNDI(2HD)T. These results suggest that our methodwill contribute to advanced organic devices using ambient p-and n-type doping in various applications, including thermoelec-tric generators and those requiring low-work-function yet sta-ble electron transporting layers. Furthermore, the observed elec-tron transfer between biomolecules and semiconductors opensnew possibilities for achieving energy storage, transfer, andconversion.4. Experimental SectionSample Fabrication: EAGLE-XG (Corning) glass was employed for sub-strates. o-Dichlorobenzene (oDCB) was purchased from Tokyo ChemicalIndustry Co., Ltd. (TCI). PNDI(2HD)T, with an Mw of 268k, an Mn of 148kand a PDI of 1.81, was purchased from Ossila. The reducing agent D-fructose, the redox mediator FMN and the dopant salt dMesIM-Cl werepurchased from TCI. TPPA-Cl was purchased from Fujifilm Wako. KOH,K2HPO4 and acetonitrile were purchased from Nacalai Tesque Corpora-tion.PNDI(2HD)T thin films were fabricated by spin-coating. The 1 wt%polymer solution in oDCB was preheated to 100 °C for dissolution. Spin-coating was conducted at 3000 rpm for 60 s. The thin films were heated to200 °C under vacuum for solvent evaporation. The resulting PNDI(2HD)Tthin film had a thickness of 33 nm.Doping solutions were prepared by dissolving the chemicals in pHbuffer. The pH buffer was prepared by dissolving about 80 mM of KOHand about 320 mM K2HPO4 in pure water. After dissolving 1 M fructose,10 mM FMN-Na, 10 mM dMesIM-Cl or 0.1 mM TPPA-Cl in pH buffer,9 vol% acetonitrile was added.The Doping process was performed by immersing the PNDI(2HD)Tthin films into the aqueous doping solutions for three hours.Glass substrates were used for the UV-Vis absorption measurements.For electrical conductivity measurements, bottom contacts were prefab-ricated on glass substrates by thermal deposition of 3 nm Cr and 30 nmAu through shadow masks. The channel width and length were 2 mm and170 µm, respectively. For XPS and PYS measurements, glass substrateswere coated with 3 nm Cr and 30 nm Au by thermal deposition.Measurements: UV–Vis was measured with V-670 spectrophotome-ter (JASCO). Electrical conductivity was measured with 2634B SystemSourceMeter (Keithley). DO was evaluated using a DO meter HI 2040-01 (HANNA instruments) based on the polarographic mechanism. XPSwas performed using a KRATOS ULTRA 2 instrument with monochro-matic Al K𝛼 X-rays. PYS measurements were performed using the SUMIT-OMO PYS-202 instrument.Supporting InformationSupporting Information is available from the Wiley Online Library or fromthe author.AcknowledgementsThis work was supported in part by JSPS KAKENHI grants (nos.JP23K23428, JP22H04959, JP23H05459, JP25H00898). This work wasSmall 2025, 21, e09278 © 2025 The Author(s). Small published by Wiley-VCH GmbHe09278 (6 of 7) 16136829, 2025, 49, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202509278 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comsupported in part by JST, CREST (no. JPMJCR21O3) and FOREST (no. JP-MJFR236R). The DFT calculations in this study were performed on theNumerical Materials Simulator at NIMS.Conflict of InterestThe authors declare no conflicts of interests.Data Availability StatementThe data that support the findings of this study are available in thesupplementary material of this article.Keywordschemical doping, electron transfer, organic semiconductorReceived: August 1, 2025Revised: October 10, 2025Published online: October 30, 2025[1] G. Wang, F. S. Melkonyan, A. Facchetti, T. J. Marks, Angew. Chem., Int.Ed. 2019, 58, 4129.[2] Z. Genene, W. Mammo, E. Wang, M. R. Andersson, Adv. Mater. 2019,31, 1807275.[3] Y. Lin, Y. Firdaus, M. I. Nugraha, F. Liu, S. Karuthedath, A.-H.Emwas, W. Zhang, A. Seitkhan, M. Neophytou, H. Faber, E. Yengel, I.McCulloch, L. Tsetseris, F. Laquai, T. D. Anthopoulos, Adv. Sci. 2020,7, 1903419.[4] Y. Lin, M. I. Nugraha, Y. Firdaus, A. D. Scaccabarozzi, F. Aniés, A.-H.Emwas, E. Yengel, X. Zheng, J. Liu, W. Wahyudi, E. Yarali, H. Faber,O. M. Bakr, L. 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See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.com Biochemical Pathways for n-Type Doping: An Electron Transfer Relay from Saccharide to Organic Semiconductors 1. Introduction 2. Results and Discussion 2.1. n-Type Chemical Doping in Aqueous Solutions 2.2. Identification of Introduced Molecular Cations 2.3. Stability of Doped State in Air at High Temperatures 3. Conclusion 4. Experimental Section Supporting Information Acknowledgements Conflict of Interest Data Availability Statement Keywords