@article{wilmington_ardekani_rustagi_bataller_kemper_younts_gundogdu_2021, title={Fermi liquid theory sheds light on hot electron-hole liquid in 1L-MoS2}, volume={103}, ISSN={["2469-9969"]}, url={https://doi.org/10.1103/PhysRevB.103.075416}, DOI={10.1103/PhysRevB.103.075416}, abstractNote={Room-temperature electron-hole liquid has recently been experimentally identified in low-dimensional transition metal dichalcogenides. Here, the authors demonstrate that a first-principles Fermi liquid model effectively predicts the photoluminescence response of this phenomenon. Using density functional theory, in conjunction with previous Raman and photoluminescence spectroscopy results, they present a consistent quantitative picture of the electron-hole liquid phase transition in suspended, heat-strained 1$L$-MoS${}_{2}$ monolayers. They show a 23-fold increase in photoluminescence per unit of direct gap carrier density and 9:1 indirect-direct hole population ratio at high strain.}, number={7}, journal={PHYSICAL REVIEW B}, author={Wilmington, R. L. and Ardekani, H. and Rustagi, A. and Bataller, A. and Kemper, A. F. and Younts, R. A. and Gundogdu, K.}, year={2021}, month={Feb} }
 @article{yu_bataller_younts_yu_li_puretzky_geohegan_gundogdu_cao_2019, title={Room-Temperature Electron-Hole Liquid in Monolayer MoS2}, volume={13}, ISSN={["1936-086X"]}, DOI={10.1021/acsnano.9b04124}, abstractNote={Excitons in semiconductors are usually non-interacting and behave like an ideal gas, but may condense to a strongly-correlated liquid-like state, i.e. electron-hole liquid (EHL), at high density and appropriate temperature. EHL is a macroscopic quantum state with exotic properties and represents the ultimate attainable charge excitation density in steady states. It bears great promise for a variety of fields such as ultrahigh-power photonics and quantum science and technology. However, the condensation of gas-like excitons to EHL has often been restricted to cryogenic temperatures, which significantly limits the prospect of EHL for use in practical applications. Herein we demonstrate the formation of EHL at room temperature in monolayer MoS2 by taking advantage of the monolayer's extraordinarily strong exciton binding energy. This work demonstrates the potential for the liquid-like state of charge excitations to be a useful platform for the studies of macroscopic quantum phenomena and the development of optoelectronic devices.}, number={9}, journal={ACS NANO}, author={Yu, Yiling and Bataller, Alexander W. and Younts, Robert and Yu, Yifei and Li, Guoqing and Puretzky, Alexander A. and Geohegan, David B. and Gundogdu, Kenan and Cao, Linyou}, year={2019}, month={Sep}, pages={10351–10358} }
 @article{younts_danilov_gundogdu_gautam_2018, title={Charge generation dynamics in polymer nonfullerene solar cells with low energy loss}, volume={8}, ISSN={["1947-7988"]}, DOI={10.1117/1.JPE.8.032209}, abstractNote={Abstract. Polymer nonfullerene solar cells are emerging as an alternative of polymer fullerene solar cells. However, maximizing the short-circuit density and open-circuit voltage is a critical issue in these solar cells. Here, using ultrafast spectroscopy, we measured exciton relaxation and charge separation dynamics in polymer nonfullerene blend with low driving force. Our study indicates high polaron yield despite the energy loss of as low as 0.59 eV. This suggests that the small driving force has minimum detrimental effect in realizing high performance in polymer nonfullerene solar cells.}, number={3}, journal={JOURNAL OF PHOTONICS FOR ENERGY}, author={Younts, Robert and Danilov, Evgeny and Gundogdu, Kenan and Gautam, Bhoj}, year={2018} }
 @article{awartani_gautam_zhao_younts_hou_gundogdu_ade_2018, title={Polymer non-fullerene solar cells of vastly different efficiencies for minor side-chain modification: impact of charge transfer, carrier lifetime, morphology and mobility}, volume={6}, ISSN={["2050-7496"]}, url={https://doi.org/10.1039/C7TA01746D}, DOI={10.1039/c7ta01746d}, abstractNote={The performance of the 11.25% efficient PBDB-T : ITIC system degraded to 4.35% after a minor side-chain modification in PBDB-O : ITIC. In this study, the underlying reasons behind this vast difference in efficiencies are investigated.}, number={26}, journal={JOURNAL OF MATERIALS CHEMISTRY A}, publisher={Royal Society of Chemistry (RSC)}, author={Awartani, Omar M. and Gautam, Bhoj and Zhao, Wenchao and Younts, Robert and Hou, Jianhui and Gundogdu, Kenan and Ade, Harald}, year={2018}, month={Jul}, pages={12484–12492} }
 @article{gautam_younts_carpenter_ade_gundogdu_2018, title={The Role of FRET in Non-Fullerene Organic Solar Cells: Implications for Molecular Design}, volume={122}, ISSN={["1089-5639"]}, url={https://doi.org/10.1021/acs.jpca.7b12807}, DOI={10.1021/acs.jpca.7b12807}, abstractNote={Non-fullerene acceptors (NFAs) have been demonstrated to be promising candidates for highly efficient organic photovoltaic (OPV) devices. The tunability of absorption characteristics of NFAs can be used to make OPVs with complementary donor-acceptor absorption to cover a broad range of the solar spectrum. However, both charge transfer from donor to acceptor moieties and energy (energy) transfer from high-bandgap to low-bandgap materials are possible in such structures. Here, we show that when charge transfer and exciton transfer processes are both present, the coexistence of excitons in both domains can cause a loss mechanism. Charge separation of excitons in a low-bandgap material is hindered due to exciton population in the larger bandgap acceptor domains. Our results further show that excitons in low-bandgap material should have a relatively long lifetime compared to the transfer time of excitons from higher bandgap material in order to contribute to the charge separation. These observations provide significant guidance for design and development of new materials in OPV applications.}, number={15}, journal={JOURNAL OF PHYSICAL CHEMISTRY A}, publisher={American Chemical Society (ACS)}, author={Gautam, Bhoj R. and Younts, Robert and Carpenter, Joshua and Ade, Harald and Gundogdu, Kenan}, year={2018}, month={Apr}, pages={3764–3771} }
 @article{younts_duan_gautam_saparov_liu_mongin_castellano_mitzi_gundogdu_2017, title={Efficient generation of long-lived triplet excitons in 2D hybrid perovskite}, volume={29}, number={9}, journal={Advanced Materials}, author={Younts, R. and Duan, H. S. and Gautam, B. and Saparov, B. and Liu, J. and Mongin, C. and Castellano, F. N. and Mitzi, D. B. and Gundogdu, K.}, year={2017} }
 @article{cho_han_younts_lee_gautam_lee_lee_kim_kim_gundogdu_et al._2017, title={Impact of highly crystalline, isoindigo-based small-molecular additives for enhancing the performance of all-polymer solar cells}, volume={5}, ISSN={["2050-7496"]}, url={https://doi.org/10.1039/C7TA06939A}, DOI={10.1039/c7ta06939a}, abstractNote={We have developed a simple yet versatile approach for enhancing the performance of all-polymer solar cells (all-PSCs) using a highly crystalline small-molecular additive, 6,6′-dithiopheneisoindigo (DTI).}, number={40}, journal={JOURNAL OF MATERIALS CHEMISTRY A}, publisher={Royal Society of Chemistry (RSC)}, author={Cho, Han-Hee and Han, Gibok and Younts, Robert and Lee, Wonho and Gautam, Bhoj R. and Lee, Seungjin and Lee, Changyeon and Kim, Taesu and Kim, Felix Sunjoo and Gundogdu, Kenan and et al.}, year={2017}, month={Oct}, pages={21291–21299} }
 @article{kim_younts_lee_lee_gundogdu_kim_2017, title={Impact of the photo-induced degradation of electron acceptors on the photophysics, charge transport and device performance of all-polymer and fullerene-polymer solar cells}, volume={5}, ISSN={["2050-7496"]}, url={https://doi.org/10.1039/C7TA07535A}, DOI={10.1039/c7ta07535a}, abstractNote={We report a comparative study of the photo-stabilities of all-polymer and fullerene-polymer solar cells based on the same polymer donor.}, number={42}, journal={JOURNAL OF MATERIALS CHEMISTRY A}, publisher={Royal Society of Chemistry (RSC)}, author={Kim, Taesu and Younts, Robert and Lee, Wonho and Lee, Seungjin and Gundogdu, Kenan and Kim, Bumjoon J.}, year={2017}, month={Nov}, pages={22170–22179} }
 @article{gautam_younts_li_yan_danilov_klump_constantinou_so_you_ade_et al._2016, title={Charge photogeneration in organic photovoltaics: Role of hot versus cold charge-transfer excitons}, volume={6}, DOI={10.1002/aenm.201670002}, abstractNote={In article number 1501032, Kenan Gundogdu and co-workers present hot and cold exciton charge separation at the polymer/fullerene interface. On the left of the image high energy photons create excitons with excess energy. On the right of the image low energy photons create solely low energy charge transfer excitons. Both types separate into free charges effectively.}, number={1}, journal={Advanced Energy Materials}, author={Gautam, B. R. and Younts, R. and Li, W. T. and Yan, L. and Danilov, E. and Klump, E. and Constantinou, I. and So, Franky and You, W. and Ade, H. and et al.}, year={2016} }
 @article{uddin_kim_younts_lee_gautam_choi_wang_gundogdu_kim_woo_et al._2016, title={Controlling Energy Levels and Blend Morphology for All-Polymer Solar Cells via Fluorination of a Naphthalene Diimide-Based Copolymer Acceptor}, volume={49}, ISSN={["1520-5835"]}, DOI={10.1021/acs.macromol.6b01414}, abstractNote={We investigate the photovoltaic properties and charge dynamics of all polymer solar cells (all-PSCs) based on 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)) and its fluorinated analogue, poly[(N,N′-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-5,5′-(3,3′-difluoro-2,2′-bithiophene)] (P(NDI2OD-T2F)), as the acceptor polymer and poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-alt-5-octyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione] (PBDTTTPD) as the donor polymer. The PBDTTTPD:P(NDI2OD-T2)-based device has a high open-circuit voltage (VOC) of 1.03 V but suffers from low power conversion efficiency (PCE) of 2.02% with a short-circuit current density (JSC) and fill factor (FF) of 4.45 mA cm–2 and 0.44, respectively. In a stark contrast, the PCE of PBDTTTPD:P(NDI2OD-T2F)-based PSC dramatically increases to 6.09% (VOC = 1.00 V, JSC = 11.68 mA cm–2, and FF = 0.52). These results are attributed...}, number={17}, journal={MACROMOLECULES}, author={Uddin, M. A. and Kim, Y. and Younts, R. and Lee, W. and Gautam, B. and Choi, J. and Wang, C. and gundogdu and Kim, B. J. and Woo, H. Y. and et al.}, year={2016}, month={Sep}, pages={6374–6383} }
 @article{cheema_younts_gautam_gundogdu_el-shafei_2016, title={Design and synthesis of BODIPY sensitizers with long alkyl chains tethered to N-carbazole and their application for dye sensitized solar cells}, volume={184}, ISSN={["1879-3312"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84994504448&partnerID=MN8TOARS}, DOI={10.1016/j.matchemphys.2016.09.024}, abstractNote={In this study, three boron dipyrromethenes (BODIPY) dyes with extended conjugation and electron donating carbazole groups with different alkyl chain lengths tethered to N-carbazole were synthesized and characterized for dye-sensitized solar cells. The goal was to study the effect of different alkyl chain lengths on dye aggregation at TiO2 surface. The proposed molecular strategy resulted in BODIPY dyes which showed interesting electronic absorption and fluorescence properties. It was observed that intramolecular energy transfer decreases with the increase in alkyl chain length possibly due to induced changes in molecular geometry caused by long alkyl chains. Additionally, interface analysis by impedance spectroscopy in comparison to N719 sensitized TiO2 solar cell showed significant charge transport related losses (Nyquist plot) most likely due to impedance resulted from aggregated BODIPY dye on TiO2 surface. Femtosecond transient absorption studies showed the loss of excited electrons by recombination with oxidized ground state of the sensitizers.}, journal={MATERIALS CHEMISTRY AND PHYSICS}, author={Cheema, Hammad and Younts, Robert and Gautam, Bhoj and Gundogdu, Kenan and El-Shafei, Ahmed}, year={2016}, month={Dec}, pages={57–63} }
 @article{dunlap-shohl_younts_gautam_gundogdu_mitzi_2016, title={Effects of Cd Diffusion and Doping in High-Performance Perovskite Solar Cells Using CdS as Electron Transport Layer}, volume={120}, ISSN={["1932-7455"]}, DOI={10.1021/acs.jpcc.6b05406}, abstractNote={Perovskite solar cells with stabilized power conversion efficiency exceeding 15% have been achieved, using a methylammonium lead iodide (MAPbI3) absorber and CdS as the electron transport layer. X-ray photoelectron spectroscopy reveals a small presence of Cd at the surface of most perovskite films fabricated on CdS. Perovskite films were deliberately doped with Cd to understand the possible impacts of Cd diffusion into the perovskite absorber layer. Doping substantially increases the grain size of the perovskite films but also reduces device performance through the formation of an electrical barrier, as inferred by the S-shape of their J–V curves. Time-resolved photoluminescence measurements of the doped films do not indicate substantial nonradiative recombination due to bulk defects, but a secondary phase is evident in these films, which experiments have revealed to be the organic–inorganic hybrid material methylammonium cadmium iodide, (CH3NH3)2CdI4. It is further demonstrated that this compound can for...}, number={30}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Dunlap-Shohl, Wiley A. and Younts, Robert and Gautam, Bhoj and Gundogdu, Kenan and Mitzi, David B.}, year={2016}, month={Aug}, pages={16437–16445} }
 @article{bondarev_popescu_younts_hoffman_mcafee_dougherty_gundogdu_ade_2016, title={Lowest energy Frenkel and charge transfer exciton intermixing in one-dimensional copper phthalocyanine molecular lattice}, volume={109}, ISSN={["1077-3118"]}, DOI={10.1063/1.4968821}, abstractNote={We report the results of the combined experimental and theoretical studies of the low-lying exciton states in crystalline copper phthalocyanine. We derive the eigen energy spectrum for the two lowest intramolecular Frenkel excitons coupled to the intermolecular charge transfer exciton state and compare it with temperature dependent optical absorption spectra measured experimentally, to obtain the parameters of the Frenkel-charge-transfer exciton intermixing. The two Frenkel exciton states are spaced apart by 0.26 eV, and the charge transfer exciton state is 50 meV above the lowest Frenkel exciton. Both Frenkel excitons are strongly mixed with the charge transfer exciton, showing the coupling constant 0.17 eV which agrees with earlier experimental measurements. These results can be used for the proper interpretation of the physical properties of crystalline phthalocyanines.}, number={21}, journal={APPLIED PHYSICS LETTERS}, author={Bondarev, I. V. and Popescu, A. and Younts, R. A. and Hoffman, B. and McAfee, T. and Dougherty, D. B. and Gundogdu, K. and Ade, H. W.}, year={2016}, month={Nov} }
 @article{cheema_younts_ogbose_gautam_gundogdu_el-shafei_2015, title={A femtosecond study of the anomaly in electron injection for dye-sensitized solar cells: the influence of isomerization employing Ru(II) sensitizers with anthracene and phenanthrene ancillary ligands}, volume={17}, ISSN={["1463-9084"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84949117754&partnerID=MN8TOARS}, DOI={10.1039/c4cp04741a}, abstractNote={HD-7 is prone to ISC and shows a continuous increase in the triplet TA signal, whereas HD-8 shows enhanced singlet injection, followed by decay in the TA signal.}, number={4}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Cheema, Hammad and Younts, Robert and Ogbose, Louis and Gautam, Bhoj and Gundogdu, Kenan and El-Shafei, Ahmed}, year={2015}, month={Jan}, pages={2750–2756} }
 @article{gautam_lee_younts_lee_danilov_kim_gundogdu_2015, title={Charge Generation Dynamics in Efficient All-Polymer Solar Cells: Influence of Polymer Packing and Morphology}, volume={7}, ISSN={["1944-8244"]}, DOI={10.1021/acsami.5b08531}, abstractNote={All-polymer solar cells exhibit rapid progress in power conversion efficiency (PCE) from 2 to 7.7% over the past few years. While this improvement is primarily attributed to efficient charge transport and balanced mobility between the carriers, not much is known about the charge generation dynamics in these systems. Here we measured exciton relaxation and charge separation dynamics using ultrafast spectroscopy in polymer/polymer blends with different molecular packing and morphology. These measurements indicate that preferential face-on configuration with intermixed nanomorphology increases the charge generation efficiency. In fact, there is a direct quantitative correlation between the free charge population in the ultrafast time scales and the external quantum efficiency, suggesting not only the transport but also charge generation is key for the design of high performance all polymer solar cells.}, number={50}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Gautam, Bhoj R. and Lee, Changyeon and Younts, Robert and Lee, Wonho and Danilov, Evgeny and Kim, Bumjoon J. and Gundogdu, Kenan}, year={2015}, month={Dec}, pages={27586–27591} }
 @article{cheema_islam_han_gautam_younts_gundogdu_el-shafei_2014, title={Influence of mono versus bis-electron-donor ancillary ligands in heteroleptic Ru(II) bipyridyl complexes on electron injection from the first excited singlet and triplet states in dye-sensitized solar cells}, volume={2}, ISSN={["2050-7496"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84905571530&partnerID=MN8TOARS}, DOI={10.1039/c4ta01942c}, abstractNote={A novel Ru(ii) bipyridyl complex was designed for DSCs.}, number={34}, journal={JOURNAL OF MATERIALS CHEMISTRY A}, author={Cheema, Hammad and Islam, Ashraful and Han, Liyuan and Gautam, Bhoj and Younts, Robert and Gundogdu, Kenan and El-Shafei, Ahmed}, year={2014}, pages={14228–14235} }
 @article{cheema_islam_younts_gautam_bedja_gupta_han_gundogdu_el-shafei_2014, title={More stable and more efficient alternatives of Z-907: carbazole-based amphiphilic Ru(II) sensitizers for dye-sensitized solar cells}, volume={16}, ISSN={["1463-9084"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84911879802&partnerID=MN8TOARS}, DOI={10.1039/c4cp04120h}, abstractNote={Here we report two novel amphiphilic Ru(ii) heteroleptic bipyridyl complexes, HD-14 and HD-15, compared to previously reported NCSU-10.}, number={48}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Cheema, Hammad and Islam, Ashraful and Younts, Robert and Gautam, Bhoj and Bedja, Idriss and Gupta, Ravindra Kumar and Han, Liyuan and Gundogdu, Kenan and El-Shafei, Ahmed}, year={2014}, pages={27078–27087} }