Neil Mallo, Shaun McAnally, Hui Jin, Eucalyptus Brooks, Ronan Chu, Mohammad Babazadeh, James Smyth, David M. Huang, Nicholas Hight-Huf, Obadiah G. Reid, Garry Rumbles, Paul L. Burn, Ian R. Gentle, Paul E. Shaw
{"title":"Free-Charge Carrier Generation in Homojunction Non-Polymeric Organic Semiconductor Films – The Role of the Optical Frequency Dielectric Constant","authors":"Neil Mallo, Shaun McAnally, Hui Jin, Eucalyptus Brooks, Ronan Chu, Mohammad Babazadeh, James Smyth, David M. Huang, Nicholas Hight-Huf, Obadiah G. Reid, Garry Rumbles, Paul L. Burn, Ian R. Gentle, Paul E. Shaw","doi":"10.1002/adom.202401825","DOIUrl":null,"url":null,"abstract":"<p>Engineering the dielectric constant (<i>ε</i>) to lower the exciton binding energy of the light-absorbing semiconductor can improve organic photovoltaic (OPV) device performance. Here, a series of materials are reported with 2-(3-oxo-2,3-dihydro-1<i>H</i>-inden-1-ylidene)malononitrile (INCN) acceptor end groups and a central glycolated bis(4<i>H</i>-cyclopenta[2,1-<i>b</i>:3,4-<i>b</i>′]dithiophene) unit with large low-frequency (<i>ε</i><sub>lf</sub> = 7.4–7.9 at 0.1–0.2 MHz) and optical-frequency (<i>ε</i><sub>opt</sub> up to 6.6 at 2 × 10<sup>14</sup> Hz) dielectric constants. The INCN end groups differed in whether they were protonated, chlorinated, or fluorinated, with the latter having the highest <i>ε</i><sub>opt</sub>. An <i>ε</i><sub>opt</sub> of 6.6 is predicted to lead to a low exciton binding energy of ≈0.04 eV. Time-resolved microwave conductivity measurements showed a temperature-dependent yield–mobility product, with it increasing linearly from 340 K. The onset temperature was near that required to overcome the calculated exciton binding energy and indicates increased free charge generation in a homojunction film. Room temperature transient absorption spectroscopy revealed that photoexcitation rapidly converted to a lower energy state that was consistent with the formation of polarons or a charge transfer state. This work provides experimental evidence of the importance of <i>ε</i><sub>opt</sub> for the generation of free charges, and a strategy for development of efficient single chromophore homojunction OPV devices.</p>","PeriodicalId":116,"journal":{"name":"Advanced Optical Materials","volume":"12 36","pages":""},"PeriodicalIF":8.0000,"publicationDate":"2024-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Advanced Optical Materials","FirstCategoryId":"88","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1002/adom.202401825","RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"MATERIALS SCIENCE, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
Engineering the dielectric constant (ε) to lower the exciton binding energy of the light-absorbing semiconductor can improve organic photovoltaic (OPV) device performance. Here, a series of materials are reported with 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (INCN) acceptor end groups and a central glycolated bis(4H-cyclopenta[2,1-b:3,4-b′]dithiophene) unit with large low-frequency (εlf = 7.4–7.9 at 0.1–0.2 MHz) and optical-frequency (εopt up to 6.6 at 2 × 1014 Hz) dielectric constants. The INCN end groups differed in whether they were protonated, chlorinated, or fluorinated, with the latter having the highest εopt. An εopt of 6.6 is predicted to lead to a low exciton binding energy of ≈0.04 eV. Time-resolved microwave conductivity measurements showed a temperature-dependent yield–mobility product, with it increasing linearly from 340 K. The onset temperature was near that required to overcome the calculated exciton binding energy and indicates increased free charge generation in a homojunction film. Room temperature transient absorption spectroscopy revealed that photoexcitation rapidly converted to a lower energy state that was consistent with the formation of polarons or a charge transfer state. This work provides experimental evidence of the importance of εopt for the generation of free charges, and a strategy for development of efficient single chromophore homojunction OPV devices.
期刊介绍:
Advanced Optical Materials, part of the esteemed Advanced portfolio, is a unique materials science journal concentrating on all facets of light-matter interactions. For over a decade, it has been the preferred optical materials journal for significant discoveries in photonics, plasmonics, metamaterials, and more. The Advanced portfolio from Wiley is a collection of globally respected, high-impact journals that disseminate the best science from established and emerging researchers, aiding them in fulfilling their mission and amplifying the reach of their scientific discoveries.