In‐situ Crosslinking and n‐Doping of Semiconducting Polymers and Their Application as Efficient Electron‐Transporting Materials in Inverted Polymer Solar Cells

Abstract

In this study, we demonstrate in‐situ n‐doping and crosslinking of semiconducting polymers as efficient electron‐transporting materials for inverted configuration polymer solar cells. The semiconducting polymers were crosslinked with bis(perfluorophenyl) azide (bis‐PFPA) to form a robust solvent‐resistant film, thereby preventing solvent‐induced erosion during subsequent solution‐based device processing. In addition, chemical n‐doping of semiconducting polymers with (4‐(1,3‐dimethyl‐2,3‐dihydro‐1H‐benzoimidazol‐2‐yl)phenyl)dimethylamine (N‐DMBI) substantially improved the power conversion efficiency of solar cells from 0.69% to 3.42%. These results open the way for progress on generally applicable polymeric interface materials, providing not only high device performance but also an effective fabrication method for solution‐processed multilayer solar cell devices.

Anion-induced N-doping of naphthalenediimide polymer semiconductor in organic thin-film transistors

“…With small amounts (0.025 eq.) of TBAF dopant the EPR signal showed a five-line pattern centred around g = 2.005, which is most likely due to hyperfine splitting by the two 14 N nuclei of the NDI…”

“…11,12 Nevertheless a few stable n-type dopants have been reported via mechanisms other than integer charge transfer. [13][14][15][16][17][18][19][20][21][22][23][24][25] For example the addition of 1H-benzimidazole or benzimidazolium salts has succeeded in tuning of the work function of graphene and the conductivity of fullerene derivatives. 13,26 Mechanistic studies in the solution phase found that the dopant reacted with the fullerene derivative through hydride or hydrogen atom transfer to afford host radical anions, which were responsible for the doping effect.…”

“…27 Comparative studies of the doping efficiency of fullerene-based OSCs with the same dopant in OTFTs also found a significant enhancement in device performance. 28 However, conjugated polymers, as the major class of solution-processable OSCs, are rarely n-doped in devices, especially OTFTs, 14,20,24,29 despite the significant improvement it can have on device parameters, e.g., charge carrier mobility, threshold voltage, channel current on/off ratio and contact resistance. Amongst the candidate conjugated n-type polymers for OTFTs, naphthalenediimide (NDI) containing copolymers have shown impressive performance to date.…”

Organic photovoltaics: Crosslinking for optimal morphology and stability

“…The result was cells that retained an impressive 90% of their initial PCE (dropping from 3.4% to just 3.0%) after 20 days storage in air [80]. Bis-azide BABP has also been used, selectively crosslinking fullerenes on mild thermal activation in blends with either P3HT, PTB7 or PDPPTBT to afford 60-90% retention of initial PCE on thermal ageing, depending on the polymer (see Table 2 for details).…”

Interfacial Layer Engineering for Performance Enhancement in Polymer Solar Cells

“…In addition to aforementioned IFL materials types, some other classes of materials have also been developed and incorporated into PSCs, mainly including self-assembly monolayers (SAMs) [121][122][123][124], crosslinked semiconducting blends [125,126], multifunctional quantum-dot monolayers [127], and inorganic salts [128]. As emerging IFLs for polymer solar cells, these materials have shown some promising characteristics for performance enhancement and stability improvement.…”