Many advances in organic photovoltaic efficiency are not yet fully understood and new insight into structure‐property relationships is required to push this technology into broad commercial use. The aim of this article is not to comprehensively review recent work, but to provide commentary on recent successes and forecast where researchers should look to enhance the efficiency of photovoltaics. By lowering the LUMO level, utilizing electron‐withdrawing substituents advantageously, and employing appropriate side chains on donor polymers, researchers can elucidate further aspects of polymer‐PCBM interactions while ultimately developing materials that will push past 10% efficiency.

As a high-performing, medium band gap donor polymer achieving over 7% in bulk heterojunction (BHJ) solar cells with a thick active layer, PBnDT-FTAZ has demonstrated unique photovoltaic properties that have not yet been fine-tuned. In this study, three new polymers (PSBnDT-FTAZ, PBnDT-SeFTAZ, and PSBnDT-SeFTAZ) are designed to determine how the FTAZ system would respond to further structural modifications. Specifically, we aimed to answer (a) whether alkylthio substitution could increase the open circuit voltage (V oc) of the related BHJ device and (b) whether selenophene incorporation could decrease the band gap of the FTAZ polymer and lead to an improved short circuit current (J sc), while PBnDT-FTAZ’s other desirable attributes (high fill factor and thick active layer) could still be retained. We found that although the V oc of the alkylthio-substituted polymers (PSBnDT-FTAZ and PSBnDT-SeFTAZ) did not appreciably increase, selenophene-incorporated polymers (PBnDT-SeFTAZ and PSBnDT-SeFTAZ) indeed showed lowered band gaps of 1.7 eV. In particular, the smaller band gap of PBnDT-SeFAZ led to a larger J sc in its BHJ solar cells than that of the original PBnDT-FTAZ solar cells. Each polymer reached moderate efficiencies (1.87–5.72%) while retaining a thick active layer (∼300 nm), demonstrating the further potential of the FTAZ system for organic photovoltaics.

This paper reports novel self-assembling T-shaped conjugated molecules based on asymmetric bisphenazines in which hexadecyloxy substituted bisphenazine is orthogonally fused with 1,4-bis(2-phenylethynyl)benzene. Tunability of one-dimensional (1D) self-assembly and electronic properties of the system was demonstrated by peripheral substitution with small functional groups. These functional groups (OCH3, H, CN) progressively reduced LUMO levels as predicted by theoretical calculations and experimentally verified by cyclic voltammetry (CV). Furthermore, the morphologies of 1D assembly were greatly influenced by the substituents. While conformational flexibility of methoxy hampered successful assembly, hydrogen and cyano substitution induced the formation of rigid microstrands and flexible nanofibers, respectively, using phase transfer methods. Detailed instrumental analyses of the 1D assembled clusters including scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) are presented. The design strategy of the new T-π-core and peripheral substitution provides a tool to control the morphology of 1D clusters with minimal structural modification of the π-core while allowing modulation of electronic properties.

In response to the structural and electronic limitations of the popular benzo[1,2-b:4,5-b′]dithiophene–thieno[3,4-b]thiophene (PBnDT–TT) polymer series, this study explores the design and synthesis of a thienothiazole (TTz) moiety. The synthesis of TTz was streamlined down to four high-yielding steps, resulting in the new polymer PBnDT–TTz for organic solar cells. By incorporating TTz, a nitrogen is directly introduced into the polymer backbone which tunes the HOMO level and eliminates the reliance on external substituents. Compared to its TT analogue, PBnDT–TTz exhibits the same HOMO level of −5.06 eV and the same V oc of 0.69 eV, yet a higher power conversion efficiency of 2.5%. These promising results demonstrate the benefits of backbone modification and the great potential of TTz in the design of new polymers for organic photovoltaics.