Processing Methods for Obtaining a Face-On Crystalline Domain Orientation in Conjugated Polymer-Based Photovoltaics

Abstract

The polymer chain orientation and degree of crystallinity within a polymer:fullerene bulk heterojunction (BHJ) photovoltaic can greatly impact device performance. In general, a face-on chain orientation is preferred for charge conduction through sandwich-structure photovoltaic devices, but for many conjugated polymers, an edge-on conformation is energetically favored. In this work, we examine the effects of different processing techniques on photovoltaics based on the poly [4,8-bis(2ethylhexyloxy)]-phenyl-C 71 -butyric-acid-methylester (PC 71 BM) materials combination. We examine the extent of polymer crystallinity and crystalline domain orientation using both traditional blend-casting (BC), where the polymer and fullerene are cast from a single, codissolved solution, as well as sequential processing (SqP), where the polymer film is deposited first, and then the fullerene is infiltrated into the polymer film in a second solution processing step. We show using two-dimensional grazing-incidence wide-angle X-ray scattering (GIWAXS) that BC leads to a disordered, isotropic polymer network in the resulting BHJ film with a correspondingly poor device efficiency. By contrast, SqP preserves the preferred face-on chain orientation seen in pure polymer films, yielding higher short-circuit currents that are consistent with the increased hole mobility of face-on oriented polymer chains. We also study the effects of the widely used processing additive 1,8-diiodooctane (DIO) on polymer chain orientation and crystallinity in photovoltaic devices made by both processing techniques. We show that DIO results in increased polymer crystallinity, and in devices made by BC, DIO also causes a partial recovery of the face-on PBDTTT-C domain orientation, improving device performance. The face-on chain orientation in SqP devices produces efficiencies similar to those of optimized BC devices made with DIO but without the need for solvent additives or other postprocessing steps.

Dodecaborane‐Based Dopants Designed to Shield Anion Electrostatics Lead to Increased Carrier Mobility in a Doped Conjugated Polymer

“…Upon doping with DDB-F 72 with low-to-mid concentration solutions (0.05 mM and 0.3 mM), we see that the edge-on orientation of P3HT's crystallites is maintained as the (010) peak is still largely in-plane, consistent with the fact that SqP is known to preserve domain orientation. [14,15,36] The in-plane data reveals a shift in the (010) peak to higher Q, reminiscent of what has been previously reported for F 4 TCNQ, [9,15] but with some significant differences.…”

“…[14,19] We expect that SqP should be amenable for use with dodecaborane clusters given that it is routinely used to infiltrate large molecules such as fullerenes and large dopants into films of conjugated polymers. [34][35][36][37][38] Here, we report the use of a newly-synthesized, strongly-oxidizing perfunctionalized DDB cluster as a dopant for the conjugated polymer P3HT. The chemical structure of our new cluster, shown in Fig.…”

Calamitic-Type Dipolar and Quadrupolar Chromophores with a Twisted Peripheral Handle: Structure–Property Outlook as Nonfullerene Acceptors for Binary Solar Cells

“…This enlargement in PCE is mainly contributed by the huge positive shift in J SC from as-cast (9.95 mA/cm 2 ) to processing (12.21 mA/cm 2 ). 80,81 In contrast, 15 showed only a minimal increment in PCE even after processing (5.42%) compared to as-cast (5.21%). Though the device performance improved after processing for unsymmetrical molecules (16 = 5.09%; 17 = 4.65%), it does not surpass the efficiencies of symmetrical analogs (14 = 6.30%; 15 = 5.42%).…”

“…Accordingly, the PCEs of 14 , 15 , 16 , and 17 increased, respectively, to 6.30%, 5.42%, 5.09%, and 4.65%, suggesting the crucial role of solvent additive in increasing the photocurrent. − In particular, the extent of increase in PCE is much greater in 14 after processing (6.30%) compared to that as-cast (5.42%). This enlargement in PCE is mainly contributed by the huge positive shift in J SC from as-cast (9.95 mA/cm 2 ) to processing (12.21 mA/cm 2 ). , In contrast, 15 showed only a minimal increment in PCE even after processing (5.42%) compared to as-cast (5.21%). Though the device performance improved after processing for unsymmetrical molecules ( 16 = 5.09%; 17 = 4.65%), it does not surpass the efficiencies of symmetrical analogs ( 14 = 6.30%; 15 = 5.42%).…”

A New Two‐Step Strategy for Encapsulating Amorphous Polymer Chains in Thiourea Crystals

“…For example, better mechanical properties are typically achieved along the direction of polymer chain alignments. [1,2] Electronic properties, [3] heat transfer efficiency, [4][5][6] and optical performance [7] of polymeric devices can also be promoted by the formation of ordered polymer chains. Therefore, controlling polymer chain alignment is highly desirable for optimization of stoichiometries reported.…”