n-Type Semiconducting Naphthalene Diimide-Perylene Diimide Copolymers: Controlling Crystallinity, Blend Morphology, and Compatibility Toward High-Performance All-Polymer Solar Cells

Abstract

Knowledge of the critical factors that determine compatibility, blend morphology, and performance of bulk heterojunction (BHJ) solar cells composed of an electron-accepting polymer and an electron-donating polymer remains limited. To test the idea that bulk crystallinity is such a critical factor, we have designed a series of new semiconducting naphthalene diimide (NDI)-selenophene/perylene diimide (PDI)-selenophene random copolymers, xPDI (10PDI, 30PDI, 50PDI), whose crystallinity varies with composition, and investigated them as electron acceptors in BHJ solar cells. Pairing of the reference crystalline (crystalline domain size Lc = 10.22 nm) NDI-selenophene copolymer (PNDIS-HD) with crystalline (Lc = 9.15 nm) benzodithiophene-thieno[3,4-b]thiophene copolymer (PBDTTT-CT) donor yields incompatible blends, whose BHJ solar cells have a power conversion efficiency (PCE) of 1.4%. However, pairing of the new 30PDI with optimal crystallinity (Lc = 5.11 nm) as acceptor with the same PBDTTT-CT donor yields compatible blends and all-polymer solar cells with enhanced performance (PCE = 6.3%, Jsc = 18.6 mA/cm(2), external quantum efficiency = 91%). These photovoltaic parameters observed in 30PDI:PBDTTT-CT devices are the best so far for all-polymer solar cells, while the short-circuit current (Jsc) and external quantum efficiency are even higher than reported values for [70]-fullerene:PBDTTT-CT solar cells. The morphology and bulk carrier mobilities of the polymer/polymer blends varied substantially with crystallinity of the acceptor polymer component and thus with the NDI/PDI copolymer composition. These results demonstrate that the crystallinity of a polymer component and thus compatibility, blend morphology, and efficiency of polymer/polymer blend solar cells can be controlled by molecular design.

Improved All-Polymer Solar Cell Performance of n-Type Naphthalene Diimide–Bithiophene P(NDI2OD-T2) Copolymer by Incorporation of Perylene Diimide as Coacceptor

“…This observation is very similar to the previous results by Jenekhe et al and could be attributed to the shorter 2-ethylhexyl side chains on PDI moiety. 18 In contrast, the π−π stacking distance increased linearly with increasing incorporation of PDI moiety into the copolymer chain ( Figure 4, inset). It increased from 3.84 Å in reference P(NDI2OD-T2) to 3.85, 3.93, and 4.00 Å in NDI-Th-PDI15, NDI-Th-PDI30, and NDI-Th-PDI50, respectively.…”

Role of Solution Structure in Self-Assembly of Conjugated Block Copolymer Thin Films

“…This goal has been met by BCPs where either one block has a conjugated backbone and the other has an insulating backbone with pendant conjugated molecules, [29][30][31][32][33][34][35][36][37] or by structures where both blocks have conjugated backbones (CBCPs). [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] Because of the relative stiffness of conjugated backbones, the phase separation of their BCP is complex due to energetic interactions between blocks, the volume fraction of the blocks, and potential crystallization.…”

Engineering of Amorphous Polymeric Insulators for Organic Field‐Effect Transistors

“…It is well known that large crystals show high stability and that the morphology stability of the active layer affects the device performance. [63][64][65][66][67][68] Aside from that, using a phase-separation strategy to achieve self-ecapsulation has also been found to be very effective. In 2008, Kang et al used this method and mixed TIPS-pentacene with two different molecular weight PαMS ( Figure 5).…”