Influence of Interface Doping on Charge-Carrier Mobilities and Sub-Bandgap Absorption in Organic Solar Cells

Abstract

P3HT:PCBM (poly(3-hexylthiophene-2,5-diyl): ([6,6]-phenyl-C61-butyric acid methyl ester)-based bulk heterojunctions (BHJs) were doped by using 4-toluenesulfonic acid (TSA) as dopant. This approach was inspired by the well-known interfacial doping of the active layer via the electron-blocking layer PEDOT:PSS (poly(3,4-ethylenedioxy-thiophene):poly-(styrenesulfonate)) at its interface. TSA is amphiphilic, acidic, and structurally very similar to the monomeric building block of PSS. Upon TSA doping, a notable increase in the light absorption in the sub-bandgap region of pristine P3HT was observed. These features are assigned to polaron transitions within P3HT; however, the TSA impact on polaron absorption features in the BHJ is rather small. Although, for small TSA concentrations and thick active layers (∼220 nm) the fill factor of the solar cells improved dramatically with increasing TSA content in the active layer, which is discussed in terms of contact resistances at interfaces in the present paper. For 0.5% TSA concentration in the active layer solution the maximum of the power conversion efficiency was obtained. At the same time, the reproducibility of solar cell performance parameters was considerably improved.

Impact of P3HT materials properties and layer architecture on OPV device stability

“…A custom-made setup for photothermal deflection spectroscopy (PDS) was used to determine the sub-bandgap absorption of all investigated P3HT films as done in previous works 69,70,71 . The measurement principle and basic setup of PDS is described elsewhere.…”

“…The sub-bandgap absorption of the P3HT batches show several known features. The first one is the peak centered at around 1000 nm which can be assigned to the P2 polaron transition 70 , indicating minor p-doping of all batches of the pristine P3HT. It seems that this is most pronounced for P3HT-IV, and least pronounced for P3HT-I and -III.…”

Lewis Acid Doping Induced Synergistic Effects on Electronic and Morphological Structure for Donor and Acceptor in Polymer Solar Cells

“…[1][2][3][4][5] Introducing the molecular dopants into the active layer or fabrication process can further tune the electronic properties of organic semiconductors, and have recently attracted interest in OSCs. [6][7][8][9][10][11][12][13][14][15][16] The beneficial effects of doped OSCs have been reported and attributed to increased charge transport, favorable formation of photo-generated carriers, and trap filling. [6][7][8][9][10][11][12][13][14][15][16] Although the benefits are obvious, the success of molecular doping is very limited in OSCs.…”

Controlling Intermolecular Interactions at Interfaces: Case of Supramolecular Tuning of Fullerene's Electronic Structure

“…Spectroscopic Methods : For electronic absorption measurements, both a UV–vis (Varian: Cary 5000) spectrophotometer in transmission mode and a custom‐made setup for photothermal deflection spectroscopy (PDS) were employed . The monochromatic light source of the PDS setup was obtained from LOT‐Quantum Design and consists of a 450 W Xe lamp and a monochromator with a focal length of 260 mm.…”