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To date, nonfullerene acceptors for organic solar cells have yet to reach the overall device performance achieved with fullerene derivatives. Power conversion efficiencies are low, even when combined with narrow optical gap polymers, with the processing conditions and blend microstructure difficult to optimize. To understand the potential origins of the decreased performance, we performed a photophysical study on a model system of blends of poly(3-n-hexyl­thiophene) (P3HT) with the planar small molecule electron acceptor 2-[{7-(9,9-di-n-propyl-9H-fluoren-2-yl)­benzo[c]­[1,2,5]­thiadiazol-4-yl}­methylene]­malononitrile (K12), focusing, in particular, on the effects of the crystallinity of the K12 phase on exciton dissociation and charge generation. Our results show that the microstructure of the blends can be manipulated by the processing conditions to give amorphous through to (semi)­crystalline films. The amorphous blends show strong quenching of the photoluminescence, which indicates that there is a fine mixture of P3HT and K12. After annealing, the blends all showed increased photoluminescence and signs of phase separation with the formation of large-scale crystalline K12 domains. Photoinduced absorption spectroscopy confirmed the presence of positive polarons in the P3HT and revealed triplet excitons in blends containing crystalline K12 domains, indicating that exciton harvesting from the K12 phase was inefficient. However, charge generation in the 1:2 blend (the best for devices) was enhanced in the (semi)­crystalline films, which suggests that aggregation of the P3HT and K12 aids charge separation. Hence, the complex phase behavior of K12 results in a trade-off between charge generation and collection against exciton harvesting from the K12 phase.

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Sponsored and Published by SPIEDownloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 5/11/2018 Terms of Use: https://www.spiedigitallibrary.org/terms-of-useThe papers included in this volume were part of the technical conference cited on the cover and title page. Papers were selected and subject to review by the editors and conference program committee. Some conference presentations may not be available for publication. The papers published in these proceedings reflect the work and thoughts of the authors and are published herein as submitted. The publisher is not responsible for the validity of the information or for any outcomes resulting from reliance thereon.Please use the following format to cite material from this book:Author ( Copying of material in this book for internal or personal use, or for the internal or personal use of specific clients, beyond the fair use provisions granted by the U.S. Copyright Law is authorized by SPIE subject to payment of copying fees. The Transactional Reporting Service base fee for this volume is $18.00 per article (or portion thereof), which should be paid directly to the Copyright Clearance Center (CCC), 222 Rosewood Drive, Danvers, MA 01923. Payment may also be made electronically through CCC Online at copyright.com. Other copying for republication, resale, advertising or promotion, or any form of systematic or multiple reproduction of any material in this book is prohibited except with permission in writing from the publisher. The CCC fee code is 0277-786X/09/$18.00.Printed in the United States of America.Publication of record for individual papers is online in the SPIE Digital Library. SPIEDigitalLibrary.orgPaper Numbering: Proceedings of SPIE follow an e-First publication model, with papers published first online and then in print and on CD-ROM. Papers are published as they are submitted and meet publication criteria. A unique, consistent, permanent citation identifier (CID) number is assigned to each article at the time of the first publication. Utilization of CIDs allows articles to be fully citable as soon they are published online, and connects the same identifier to all online, print, and electronic versions of the publication. SPIE uses a six-digit CID article numbering system in which:The first four digits correspond to the SPIE volume number. The last two digits indicate publication order within the volume using a Base 36 numbering system employing both numerals and letters. These two-number sets start with 00, 01, 02, 03, 04, 05, 06, 07, 08, 09, 0A, 0B … 0Z, followed by 10-1Z, 20-2Z, etc.The CID number appears on each page of the manuscript. The complete citation is used on the first page, and an abbreviated version on subsequent pages. Numbers in the index correspond to the last two digits of the six-digit CID number.Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 5/11/2018 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use

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