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[Yu Yamashita](https://orcid.org/0000-0001-7966-3197), Shinya Kohno, Elena Longhi, Samik Jhulki, Shohei Kumagai, Stephen Barlow, Seth R. Marder, [Jun Takeya](https://orcid.org/0000-0002-7003-1350), Shun Watanabe

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[N-type molecular doping of a semicrystalline conjugated polymer through cation exchange](https://mdr.nims.go.jp/datasets/da563046-785d-4db6-bf22-6436c7adac3d)

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N-type molecular doping of a semicrystalline conjugated polymer through cation exchangecommunicationsmaterials Articlehttps://doi.org/10.1038/s43246-024-00507-2N-type molecular doping of asemicrystalline conjugated polymerthrough cation exchangeCheck for updatesYu Yamashita 1,2 , Shinya Kohno1, Elena Longhi3, Samik Jhulki3, Shohei Kumagai1, Stephen Barlow3,4,Seth R. Marder3,4,5, Jun Takeya 1,2 & Shun Watanabe 1Control of electrical doping is indispensable in any semiconductor device, and both efficient hole andelectron doping are required for many devices. In organic semiconductors, however, electron dopinghas been essentially more problematic compared to hole doping because in general organicsemiconductors have low electron affinities and require dopants with low ionization potentials that areoften air-sensitive. Here, we adapt an efficient molecular doping method, so-called ion-exchangedoping, to dope electrons in a polymeric semiconductor. We initially reduce the polymericsemiconductor using one electron transfer from molecular dopants, and then the ionized dopants inthe resulting air-unstable films are replaced with secondary ions via cation exchange. Improvedambient stability and crystallinity of the doped polymeric semiconductors are achieved when aspecificbulkymolecular cationwaschosenas the secondary ion, compared to conventionalmethods.The presented strategy can overcome the trade-off relationship between reducing capability andambient stability in molecular dopants, and a wider selection of dopant ions will help to realizeambient-stable electron conductors.Impurity doping of semiconductors is essential for most semiconductordevices, and the pn junction and complementary metal-oxide-semiconductor inverter are indispensable building blocks for devicesmanufactured today1. Likewise as in Si-based electronic devices, doping oforganic semiconductors (OSCs) has been applied in various opto-electronicdevices, such as organic light-emitting diodes2,3, organic field-effecttransistors4–6, bipolar transistors7, organic photovoltaics8,9, and organicthermoelectric devices10–13. In inorganic semiconductors, control of chargepolarity can be achieved in a straightforward way by an introduction ofatomic dopants with different valences. On the other hand, doping of OSCsis achievedby an admixture ofmolecular reductants or oxidants into hostπ-conjugatedmolecules14,15. Althoughdopantmolecules have awide variety ofsize, conformation, and reactivity, candidate n-dopants (reductants) thatachieve an efficient one-electron transfer and robust stability in material/device processing and under device operation conditions are rather limitedto date. Efficient solid-state electron transfer requires that the reductant’sionization potential (IP) is smaller than the OSC’s electron affinity (EA).Typical EAs of electron-transport OSCs range from less than 3.0 eV to ca.4.0 eV, and thus strong reducing agents are required for electron doping (n-type doping) and electron-doped states are often sensitive to atmosphericoxygen and water.A practical strategy to control the nature of ions in doped polymericsemiconductors has been demonstrated recently. Hole-doped polymericsemiconductors with various dopant anions have been explored by anionexchange and related doping methods16–22. The process of anion exchangedoping is initiated by electron transfer reactions between semiconductorsand oxidants, where the cationic semiconductors and oxidant-derivedanions form intermediate donor-acceptor ion pairs. Then, an introductionof secondary anions can give rise to a spontaneous anion exchange in thepolymeric semiconductors. The most important feature of ion-exchangedoping is the ability to separate the two fundamental requirements inmolecular dopants; the strength of redox reactivity and guarantee of chargeneutrality by self-ionization. As a reducing agent for electron doping, forinstance, cobaltocene (CoCp2)23 with reasonably low IP (4.1 eV in the solid1Material Innovation Research Center (MIRC) and Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5Kashiwanoha, Kashiwa,Chiba 277-8561, Japan. 2ResearchCenter forMaterialsNanoarchitectonics (MANA),National Institute forMaterials Science (NIMS), 1-1Namiki,Tsukuba, Ibaraki 205-0044, Japan. 3School of Chemistry and Biochemistry andCenter for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta,GA 30332-0400, USA. 4Renewable and Sustainable Energy Institute, University of Colorado Boulder, Boulder, CO 80309, USA. 5Departments of Chemistry and ofChemical and Biological Engineering, University of Colorado, Boulder, CO 80309, USA. e-mail: YAMASHITA.Yu@nims.go.jp; swatanabe@edu.k.u-tokyo.ac.jpCommunications Materials |            (2024) 5:79 11234567890():,;1234567890():,;http://crossmark.crossref.org/dialog/?doi=10.1038/s43246-024-00507-2&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s43246-024-00507-2&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s43246-024-00507-2&domain=pdfhttp://orcid.org/0000-0001-7966-3197http://orcid.org/0000-0001-7966-3197http://orcid.org/0000-0001-7966-3197http://orcid.org/0000-0001-7966-3197http://orcid.org/0000-0001-7966-3197http://orcid.org/0000-0002-7003-1350http://orcid.org/0000-0002-7003-1350http://orcid.org/0000-0002-7003-1350http://orcid.org/0000-0002-7003-1350http://orcid.org/0000-0002-7003-1350http://orcid.org/0000-0001-7377-6043http://orcid.org/0000-0001-7377-6043http://orcid.org/0000-0001-7377-6043http://orcid.org/0000-0001-7377-6043http://orcid.org/0000-0001-7377-6043mailto:YAMASHITA.Yu@nims.go.jpmailto:swatanabe@edu.k.u-tokyo.ac.jpstate)24 has been known to results in efficient but air-unstable electrondoping for n-typeOSCs25. In particular, reversible electron transfer betweenCoCp2 and n-type OSCs means equilibrium concentrations of air-sensitiveand volatile neutralCoCp2 remain indopedOSCs and canultimately lead todedoping through reaction with air and/or sublimation. If cation exchangeis applicable to CoCp2 doped OSCs, various stable and redox-inert mole-cular cations X+ could be introduced to electron-doped polymers ([OSC•−CoCp2+]→ [OSC•− X+]), while utilizing the moderately strong reducingnature of CoCp2.In this study, we developed a cation-exchange doping method thatenables the electron doping of semicrystalline polymeric semiconductorswith stable and redox-inert closed-shell cations. The doped thin films wereevaluated by UV-Vis absorption spectroscopy, elemental analysis, photo-electron spectroscopy, and electrical conductivity measurements. Ourexperimental observations supportedourmodel of cation-exchangedoping,as shown in Fig. 1a. The semiconductor thin films electron-doped via ourmethod showedambient stabilitydependingon themolecular cation speciesintroduced during ion exchange. In our study, high ambient stability wasobserved when a conjugated polymer thin film was doped with the bulky1,3-dimesitylimidazolium (dMesIM+, Fig. 1b) cation. Interestingly, the π-stacking of the polymeric semiconductorwasmaintainedupon doping onlywhen dMesIM+ was employed, while use of other cations disturbed the π-stacking. Cation exchange doping with a wide choice of dopant cations willhelp facilitate explorations of the structure-property relationships inelectron-doped OSCs.Results and discussionConfirmation of cation-exchange dopingUV-Vis measurements were employed to evaluate the doping efficiency ofourmethod in a widely studied polymeric semiconductor, poly[N,N’-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5’-(2,2’-bithiophene) (P(NDI2OD-T2))26. P(NDI2OD-T2) thin films werespin-coated on glass substrates and then thermally annealed. The thin filmswere chemically doped by immersing them in a doping solution containingcobaltocene (CoCp2) with or without salts of organic cations. All the fab-ricationprocesseswere conducted in aN2-purged glove box, and absorptionmeasurements were conducted in ambient air without encapsulation. Theabsorption spectra of a pristine (undoped) P(NDI2OD-T2) thin film isshown inFig. 1c,where the lowest energy absorptionpeak is ca. 704 nm.Thespectrum of a thin film doped using a solution containing only CoCp2 isnearly identical to that of the pristine film. Although the thin film showedcolor changes upon chemical doping in the glove box, its color returned tothat of the undoped film upon air exposure. This behavior is ascribed to thededoping of the once-electron-doped thin film upon air exposure owing tothe instability of CoCp223,25. When a combination of CoCp2 and tetra-butylammonium (TBA) chloride was employed, the features of electron-dopedP(NDI2OD-T2)25 were observed via themeasurement in ambient air(Fig. 1d), indicating that unlike the CoCp2-doped film, this thin film doesnot undergo rapid dedoping. Here, the intensity of the lowest energy exci-tation of pristine P(NDI2OD-T2) with a peak at 704 nm was decreased. Atthe same time,new featureswithpeak at 496, 696, and798 nmemerged.Thepeak observed in the pristine film at 392 nm moves to slightly shorterwavelength of 370 nm. All of these features agree with the changes in UV-Vis spectra observed during electrochemical doping of this polymer fromneutral to radical anion state27. In this study, TBA+ salts with PF6− andbis(trifluoromethanesulfonyl)imide (TFSI−) were also employed (Fig. 1d).The observed ambient stability of the doped state indicates that the anioniccharges in the doped polymer thin films are not compensated by CoCp2+but rather by TBA+ through the mechanism described in Fig. 1a. Note thatthese spectral changes were not observed when P(NDI2OD-T2) thin filmswere immersed in salt solutions without CoCp2 (Supplementary Note 2),suggesting both salts and CoCp2 play key roles. Improvements in theambient stability of all the employed counter-anions imply that this phe-nomenon is not a anion-specific reaction but likely to be an ion-exchangereaction where anions simply serve as spectator ions. Combinations ofCoCp2 and the bulky organic cations of tetraphenylphosphonium (TPP+)and dMesIM+ were also tested; in this case, absorption spectra similar tothose obtainedwith the TBA+ salts were obtained (Fig. 1e).While a pristineX+Y−Y− X+CoCp2e−ac de−X+Y−Co CoCoSSN OOC HO N OnCC HC HP(NDI2OD-T2)electrontransfercationexchangeCoCp  + salttreatedTBA-ClTBA-PF6TBA-TFSIbTBA+NNS SCFFC OOOO–TFSI–PFFFFFFPF –Cl–Y–X+N N+–+dMesIM+TPP+Absorbance (a.u.)Wavelength (nm) pristine CoCp2 treatedWavelength (nm)1600120080040016001200800400TPP-CldMesIM-ClAbsorbance (a.u.)Absorbance (a.u.)eCoCp  + salttreatedWavelength (nm)16001200800400P+Fig. 1 | Cation-exchange doping. a Illustration of the cation-exchange dopingprocess. b Chemical structures of the employed ionic compounds. c UV-Visabsorption spectra of pristine andCoCp2-doped P(NDI2OD-T2) thin films. UV-Visabsorption spectra of P(NDI2OD-T2) thin films processed with combinations of (d)CoCp2 and TBA+ salts (e) CoCp2 and TPP+ or dMesIM+ salts. UV-Vis spectra wereall acquired in ambient air. The spectra are shown with offsets to improve thevisibility.https://doi.org/10.1038/s43246-024-00507-2 ArticleCommunications Materials |            (2024) 5:79 2P(NDI2OD-T2) thin film showed conductivity on the order of 10−8 S cm−1,all the samples doped with combinations of CoCp2 and salts showed con-ductivity on the orderof 10−5 S cm−1 in air,which supports that the observedchanges in UV-Vis spectra are ascribed to introduction of electrons inP(NDI2OD-T2) thin films. Detail of conductivity measurements and IVcurves are available in Supplementary Note 3.The identity of the dopant cations introduced into the P(NDI2OD-T2)thin films was further confirmed from the elemental composition revealedby X-ray photoelectron spectroscopy (XPS). Thin films of P(NDI2OD-T2)were prepared in the same manner as for the absorption measurements,except that the glass substrates were coated with Cr/Au prior to the fabri-cation of the polymer films. The undoped P(NDI2OD-T2) thin film showspeaks from C 1s, N 1s, O 1s, and S 2p which is in agreement with thechemical structure of P(NDI2OD-T2) (Fig. 2a–d) Please see SupplementaryNotes 4 and 5 for detailed peak analysis and spectra in a wide energy range.For the CoCp2-doped thin film, peaks assigned to Co 2pwere also observed(Fig. 2e). When CoCp2 and dMesIM-Cl were employed in the chemicaldoping process, the peak intensity of Co 2p normalized by that of C 1sdecreased by c.a. 87% compared with that of the CoCp2-doped sample. Inthe N 1s region, peaks from different binding energies are overlapping,which was deconvoluted to nitrogen atoms in P(NDI2OD-T2)(399.71 ± 0.02 eV) and dMesIM+ (401.63 ± 0.01 eV). The binding energy ofthe latter matches well with a literature value for a imidazolium structure28.Quantitative analysis suggests that the molar ratio of dMesIM+/P(NDI2OD-T2) monomer was 0.85, suggestive of a high doping level atleast near the surface of the film, assuming a homogeneous distribution ofdopant ions. Please see Supplementary Note 4 for detail of deconvolutionprocedures. These observations suggest that the majority of CoCp2 and itscationic form are replaced by dMesIM+ during doping. When CoCp2 andTPP-Cl were employed for chemical doping, the peak intensity of Co 2pbecame comparable with that of the dMesIM+-doped sample. A clear P 2ppeak was observed, indicating that TPP+ is present in this thin film (Fig. 2f).The molar ratio of TPP+/P(NDI2OD-T2) monomer was estimated to be1.10. Overall, the absorption, conductivity and XPSmeasurements supportthe supposition that cation exchange occurs in our chemical dopingmethod, in which P(NDI2OD-T2) thin films are mainly doped with bulkyorganic cations such as TPP+ and dMesIM+.The IP values of the cation-exchange-doped thin films were evaluatedusing photoelectron yield spectroscopy (PYS). In this method, photoelec-tron yieldwas obtainedwhile sweeping thewavelength of incidentUV light.In the analysis of the PYSmeasurements, the cube root of the photoelectronyieldwas plotted, the threshold ofwhich showed the IP values of the organicmaterials29. The IP of the undoped P(NDI2OD-T2) originates from thehighest occupied molecular orbital (HOMO) of the polymer, which isevaluated to be 5.8 eV and close to the reported value30 (Fig. 3a). When thispolymer is heavily electron-doped, a large decrease in IP is expected becauseof the filling of the lowest unoccupied molecular orbital (LUMO) withelectrons. Such large shifts in IPwere observed for theTPP+- anddMesIM+-doped thin films (Fig. 3b). The resulting IP is comparable with the knownLUMO level of this polymer30, which supports the successful electrondoping of the LUMO of P(NDI2OD-T2).Ambient stabilityThe effects of the dopant cations on the stability of the doped P(NDI2OD-T2) thin films were evaluated using UV-Vis measurements. Based on themeasured IP values, the electron-doped P(NDI2OD-T2) thin films areexpected to be dedoped under ambient conditions owing to their redoxreactions with water and oxygen2. In this study, dimeric dopants thatshowed moderate ambient stability before and after chemical doping25,31were also tested as a comparison. Dimers of 2-(4-dimethylaminophenyl)-a bIntensity(a.u.)300295290285280Binding Energy (eV)NeutralCoCp2dMesIM+TPP+Intensity(a.u.)410405400395390Binding Energy (eV)Intensity(a.u.)810800790780Binding Energy (eV)C 1s N 1sCo 2p P 2pcd540535530525172168164160Intensity(a.u. )Binding Energy (eV)Intensity( a.u.)Binding Energy (eV)O 1sS 2pIntensity a.u.)140136132128Binding Energy (eV)e fFig. 2 | Elemental analysis of the electron-doped conjugated polymers. XPS sig-nals obtained from the pristine, CoCp2-doped, and cation-exchange-dopedP(NDI2OD-T2) thin films. The names of the cation species are denoted for thecation-exchange-doped samples. The signals of the peak positions for (a) C 1s, (b) N1s, (c) O 1s, (d) S 2p, (e) Co 2p, and (f) P 2p are shown.https://doi.org/10.1038/s43246-024-00507-2 ArticleCommunications Materials |            (2024) 5:79 31,3-dimethylbenzo[d]imidazole (N-DMBI) and RuCp*Mes (Cp* =pentamethylcyclopentadienyl; Mes = 1,3,5-trimethylbenzene) were dis-solved in a doping solution without salts. In this case, N-DMBI+ andRuCp*Mes+ are thedopant cations for the electron-dopedP(NDI2OD-T2).The absorption spectra of the processed thin filmsmeasured under ambientconditions showed the features of electron doping consistent with theliterature27, demonstrating the superior ambient stability of these dopantscompared with CoCp2 (Fig. 4a, b). However, in our stability tests, the thinfilms doped with these dopants showed dedoping upon exposure to humidair of 20 °C and 80% relative humidity for 1 h. Dedoping was suggested alsofor thin films doped with TBA+ or TPP+ through cation exchange in thestability test (Fig. 4c, d). By contrast, the thin film doped with dMesIM+exhibited improved stability in humid air. The ratio of doped fraction in athinfilm, θ, was evaluated for thedMesIM+-doped sample basedon theUV-Vis spectra (Fig. 4f). θwas defined to be unity at 0 h in the durability test andcalculated based on the relative area of the peak at 509 nm that appears indoped samples. Please see Supplementary Note 6 for detail. Conductivityalso showed prolonged lifetime when using this dopant (Supplemen-tary Fig. S2).The ambient stability ofOSCs dopedwith redox-inert closed-shell ionshas recently been discussed, and the effects of the ion size16,18 and supra-molecular structures32,33 of semiconductor-dopant pairs have been reported.Given the ion-size effect and calculated volumes of dopant cations (Table 1),it is unclear why the dMesIM+-doped thin film shows higher stability thanthe films doped with other dopant cations. One possibility is that thecrystalline structure of the film affects the stability of the doped state32,33, asdiscussed below.Thin-film structuresThe crystalline structures of the electron-doped P(NDI2OD-T2) thin filmswere evaluated through X-ray scattering measurements (Fig. 5a–f), whichproved that the dopant cation species had considerable effects on thestructures. Pristine P(NDI2OD-T2) show the features of face-onorientations34 (Fig. 5a). The (h00) diffraction peaks originating from thea b0.40.30.20.10.0Absorbance12001000800600400Wavelength (nm)0.40.30.20.10.0Absorbance12001000800600400Wavelength (nm)0.40.30.20.10.0Absorbance12001000800600400Wavelength (nm)0.40.30.20.10.0Absorbance12001000800600400Wavelength (nm)0 h1 h3 h5 h18 h27 h47 h70 h0 h1 h0 h1 h0 h1 hTBA+N+dMesIM+Ru+cdNNN +N N+0.40.30.20.10.0Absorbance12001000800600400Wavelength (nm)eP+TPP+0 h1 hN-DMBI+RuCp*MesθTime (h)f 1.00.80.60.40.20.06040200Fig. 4 | Stability of the electron-doped polymer thin films under humid condi-tions.UV-vis spectra of doped P(NDI2OD-T2) thin films before and after exposureto humidity conditions of 20 °C and 80%RH.Dopingwith (a) (RuCp*Mes)2, (b) (N-DMBI)2, (c) TBA+ exchange, (d) TPP+ exchange, and (e) dMesIM+ exchange wereemployed. f Doping level θ estimated for dMesIM+-doped thin film.ab0.060.040.020.00(ynortceleotoh Pield)3/17.06.05.04.0Photon energy (eV)pristine(ynortceleo tohPield)3/10.060.040.020.004.84.44.03.63.2Photon energy (eV)TPP+ dopeddMesIM+ dopedFig. 3 | Photoelectron yield spectroscopy measurements of the electron-dopedconjugated polymers. Plots of the photoelectron yields obtained from the (a)pristine and (b) cation-exchange-doped P(NDI2OD-T2) thin films. The names ofthe cation species are denoted for the cation-exchange-doped samples.https://doi.org/10.1038/s43246-024-00507-2 ArticleCommunications Materials |            (2024) 5:79 4lamellar structures were observedmainly in the in-plane direction, whereasthe (010) peak originating from π-stacking appeared in the out-of-planedirection (Fig. 5g–j). To evaluate changes in thin-film structures uponchemical doping, the (100) peak intensity observed in the in-plane directionI(100)IP, out-of-plane direction I(100)OP, and their sum I(100)total were esti-mated (See SupplementaryNote 7 forfittings). Table 2 shows the ratio of theout-of-plane peak intensity to the total one, I(100)OP/I(100)total. TPP+-dopedfilm did not show clear diffraction peaks, which suggests disorderedstructure for this sample. TBA+-, N-DMBI+-, andRuCp*Mes+-dopedfilmsshowed values close to unity, suggesting greater fractions of the films wereedge-on orientated or the crystallinities of the edge-on oriented fractionswere higher compared to the pristine film. Note that in spin-coated filmswith randomly oriented polymer main chains, only small fractions ofpolymers with a specific angle to the incident x-ray can contribute to the in-plane direction diffraction peak, which decreases the intensity of in-plane toout-of-plane diffraction. This explains I(100)OP/I(100)total of 0.53 for thepristine film, which has been reported to be face-on oriented34. In the in-plane direction, a clear peak at 0.9Å−1 was observed for RuCp*Mes+-dopedfilm (Fig. 5j); this peak is assigned to order along the main chain direction,i.e. to a (001’) reflection34,35. This feature is consistent with a semicrystallineedge-on oriented character for the RuCp*Mes+-doped film.The dMesIM+-doped thin film exhibited a relatively small value forI(100)OP/I(100)total compared to other dopants. In addition to this, (010)π-stacking peak at 1.6Å−1 in the out-of-plane direction was maintained forthis dopant but was not observed for the other dopants around this position(Fig. 5h). This feature was not observed when other imidazolium-basedcations were used (Supplementary Note 8). The clear difference in crystal-line structures with different dopants suggests that the choice of cationspecieshas an impacton the crystalline structure,which affects the transportproperties and ambient stability of the doped states. Face-on oriented, π-stacked structures in the dMesIM+-doped thin film could contribute to theimproved ambient stability observed in our study.ConclusionIn this study, we developed the cation-exchange doping method forpolymeric semiconductors. Successful cation exchange from CoCp2 tostable and redox-inert closed-shell cations was confirmed by absorptionand XPS elemental analyses. The electron doping of the P(NDI2OD-T2)thin films was also confirmed by PYSmeasurements, where large shifts inIP were observed owing to the filling of the density of states in the LUMOof P(NDI2OD-T2). Durability under humid conditions was dramaticallyimproved by employing dMesIM+ in our method. The observed dur-ability may be affected by the crystalline structures of the doped thinfilms. X-Ray scattering measurements showed that the cation speciesexerts considerable effects on the crystallinity and orientation of theTable 1 | Volumes of dopant cation moleculesName Volume (nm3)TBA+ 0.39dMesIM+ 0.38N-DMBI+ 0.38RuCp*Mes+ 0.33TPP+ 0.46Gaussian 16 was employed to optimize structures and calculate volumes. Molecular structureswere optimized via DFT calculations based on the B3LYP functional and 6-31+G(d) basis set. TheLanl2DZ basis set was employed for RuCp*Mes+, which includes a Ru atom.aqxy (Å-1)qz (Å-1) qz (Å-1)dMesIM+(RuCp*mes)2(N-DMBI)2pristine(100)(200)(001’)in-plane in-plane (magnified)out-of-plane (magnified)out-of-plane(010)(100)intensit).u.a(ypristine N-DMIBI+ RuCp*Mes+TBA+ dMesIM+TPP+Ru+N N+NNN +P+N+g2.01.61.20.82.01.51.00.52.01.51.00.5 2.01.61.20.8intensit).u.a(yqxy (Å-1)intensit).u .a(yi ntensit).u.a(yTBA+TPP+2.01.00.0q z (Å-1)-2.0 -1.0 0.0 1.0 2.0qxy (Å-1)2.01.00.0q z (Å-1)-2.0 -1.0 0.0 1.0 2.0qxy (Å-1)2.01.00.0q z (Å-1)-2.0 -1.0 0.0 1.0 2.0qxy (Å-1)2.01.00.0q z (Å-1)-2.0 -1.0 0.0 1.0 2.0qxy (Å-1)2.01.00.0q z (Å-1)-2.0 -1.0 0.0 1.0 2.0qxy (Å-1)2.01.00.0q z (Å-1)-2.0 -1.0 0.0 1.0 2.0qxy (Å-1)b cd e fh i jFig. 5 | X-Ray scatteringmeasurements of P(NDI2OD-T2) thin films doped withvarious dopants. X-Ray scattering images of P(NDI2OD-T2) thin films (a) inpristine state and after doping with (b) (N-DMBI)2, (c) (RuCp*Mes)2, (d) TBA+exchange, (e) TPP+ exchange, (f) and dMesIM+ exchange. g, h Plots of intensitiesand their magnified versions for the out-of-plane and (i, j) the in-plane directions.https://doi.org/10.1038/s43246-024-00507-2 ArticleCommunications Materials |            (2024) 5:79 5electron-doped thin films. Our method presents new opportunities forfuture research on the structure-property relationships in doped mate-rials with various dopant cations and the development of high-performance electron-doped OSCs.MethodsThin-film fabricationHigh-purity glass substrates were employed for the optical and electricalmeasurements. Glass or Si substrates with naturally oxidized layers wereemployed for the X-ray scattering measurements. Glass substrates coatedwith Cr/Au electrodes were used for the XPS and PYS measurements.P(NDI2OD-T2) thin films were deposited via spin-coating. The resultingfilms were annealed on a hotplate at 180 °C for 30min and then slowlycooled. The thickness of the films was determined to be 70 ± 5 nm using aDektak surface profilometer. The P(NDI2OD-T2) thin filmswere doped byimmersion in the dopant solutions for 5min in an N2-purged glove box.Detailed descriptions of the film preparation and doping procedures arepresented in the Supplementary Note 1.Thin-film evaluationsUV-Vis absorption spectra were obtained in air using a V-670 (JASCO)spectrometer. Electrical conductivities were measured in air using aKeithley 2612B source meter. XPS measurements were performed usinga KRATOS ULTRA 2 instrument with monochromatic Al Kα X-rays.PYS spectra were obtained with a SUMITOMO PYS-202 system undervacuum using a turbomolecular pump system; here, a deuterium lamp(xenon lamp) was employed for the pristine (doped) thin films. 2DX-Ray scattering images were obtained using a RIGAKU SmartLabinstrument with a MicroMax-007HF X-ray generator employing Cu Kαradiation (λ = 0.15418 nm).DFT calculationsStructural optimization and evaluation of the molar volumes of the mole-cular ions were conducted using Gaussian 16 software. The B3LYP func-tional and 6-31+G(d) basis set were employed. The Lanl2DZ basis set wasemployed for RuCp*Mes+, which includes a Ru atom.Data availabilityThe data supporting the plotswithin this study are available fromZenodo athttps://doi.org/10.5281/zenodo.10911316.Received: 24 October 2023; Accepted: 16 April 2024;References1. Sze, S. M. Semiconductor Devices: Physics and Technology (Johnwiley & sons, 2008).2. 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Ishii, H., Kinjo, H., Sato, T., Machida, S.-i. & Nakayama, Y.Photoelectron yield spectroscopy for organic materials andTable 2 | Ratio of (100) diffraction peaks observed in the in-plane and out-of-plane directionsDopant I(100)OP/I(100)totalPristine 0.53 ± 0.13N-DMBI+ 0.929 ± 0.009RuCp*Mes+ 0.967 ± 0.003TBA+ 0.938 ± 0.006TPP+ –dMesIM+ 0.74 ± 0.02https://doi.org/10.1038/s43246-024-00507-2 ArticleCommunications Materials |            (2024) 5:79 6https://doi.org/10.5281/zenodo.10911316interfaces. In Electronic Processes in Organic Electronics, 131–155(Springer, 2015).30. Qi, Y. et al. Solution doping of organic semiconductors using air-stable n-dopants. Appl. Phys. Lett. 100, 54 (2012).31. Mohapatra, S. K., Marder, S. R. & Barlow, S. Organometallic andorganicdimers:Moderately air-stable, yet highly reducing, n-dopants.Acc. Chem. Res. 55, 319–332 (2022).32. Yamashita, Y. et al. 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Contributions to discussion of results and editingof the manuscript by S.B. and S.R.M. were supported by the Center for SoftPhotoElectroChemical Systems (SPECS), an Energy Frontier ResearchCenter funded by the U.S. Department of Energy, Office of Science, BasicEnergy Sciences under award No. DE-SC0023411.Author contributionsY.Y., S.W., S.B. and S.R.M. conceived the proof-of-concept of the dopingmethod. Y.Y., S.Kohno, and S.Kumagai designed and performed theexperiments and analyzed the data. E.L. and S.J. synthesized the(RuCp*Mes)2 and N-DMBI dimers. Y.Y. wrote the manuscript. S.B., S.R.M.,S.W. and J.T. supervised the work. All authors discussed the results andreviewed the manuscript.Competing interestsS.W. is an Editorial Board Member for Communications Materials and wasnot involved in the editorial review, or thedecision topublish, thisArticle. Theall other authors declare no competing interests.Additional informationSupplementary information The online version containssupplementary material available athttps://doi.org/10.1038/s43246-024-00507-2.Correspondence and requests for materials should be addressed toYu Yamashita or Shun Watanabe.Peer review informationCommunicationsMaterials thanks Ian Jacobs andthe other, anonymous, reviewer(s) for their contribution to the peer review ofthis work. Primary Handling Editors: Jet-Sing Lee.Reprints and permissions information is available athttp://www.nature.com/reprintsPublisher’s note Springer Nature remains neutral with regard tojurisdictional claims in published maps and institutional affiliations.Open Access This article is licensed under a Creative CommonsAttribution 4.0 International License, which permits use, sharing,adaptation, distribution and reproduction in anymedium or format, as longas you give appropriate credit to the original author(s) and the source,provide a link to the Creative Commons licence, and indicate if changeswere made. The images or other third party material in this article areincluded in the article’s Creative Commons licence, unless indicatedotherwise in a credit line to the material. If material is not included in thearticle’sCreativeCommons licence and your intended use is not permittedby statutory regulation or exceeds the permitted use, you will need toobtain permission directly from the copyright holder. To view a copy of thislicence, visit http://creativecommons.org/licenses/by/4.0/.© The Author(s) 2024https://doi.org/10.1038/s43246-024-00507-2 ArticleCommunications Materials |            (2024) 5:79 7https://doi.org/10.1038/s43246-024-00507-2http://www.nature.com/reprintshttp://creativecommons.org/licenses/by/4.0/ N-type molecular doping of a semicrystalline conjugated polymer through cation exchange Results and discussion Confirmation of cation-exchange�doping Ambient stability Thin-film structures Conclusion Methods Thin-film fabrication Thin-film evaluations DFT calculations Data availability References Acknowledgements Author contributions Competing interests Additional information