Dithiapyrannylidenes as Efficient Hole Collection Interfacial Layers in Organic Solar Cells

摘要

One inherent limitation to the efficiency of photovoltaic solar cells based on polymer/fullerene bulk heterojunctions (BHJs) is the accumulation of positive charges at the anodic interface. The unsymmetrical charge collection of holes and electrons dramatically decreases the short-circuit current. Interfacial layers (IFLs) such as poly(3.4-ethylenedioxythiophene):poly(4-styrenesulfonate) have no effect on the unbalanced electron/hole transport across the BHj. We report here on the use of dithiapyrannylidenes (D1TPY), a new class of planar quinoid compounds, as efficient hole-transporting/electron-blocking layers in organic solar cells based on poly(3-hexylthiophene)/[6.6]-phenyl-C_(61)-butyric acid methyl ester (P3HT.PCBM) BHJs Inserting a 15-nm-thick 1FL of 4.4'-bis(diphenyl-2,6-thiapyrannylidene) (DITPY-Ph4) between the indium-tin oxide electrode and the P3HT:PCBM BHJ prevents detrimental space-charge effects and Favors recombination-limited currents. Current-sensing atomic force microscopy reveals a drastic increase of the hole-carrying pathways in DITPY-Ph4 compared to PEDOT;PSS. In ambient conditions, photovoltaic cells using DITPY-Ph,, exhibit an 895 increase in the current density, although the conversion efficiency remains slightly lower compared to PEDOT:PSS-based devices. Finally, we present a detailed analysis of the photocurrent generation, showing that DITPY-Ph4 IFLs induce a transition from unproductive space-charge-limited currents to recombination-limited currents.