An alcohol-soluble perylene diimide derivative as cathode interfacial layer for PDI-based nonfullerene organic solar cells

• The active layer covered by PDIP layer exhibited smoother and more hydrophilic surface, thus easing inherent incompatibility at the metal/organic layer interface.
• An interfacial dipole between active layer and metal electrode was formed after introducing PDIP layer.
• The enhanced built-in potential and improved charge transport induced by PDIP optimized the final device performance.

An organic photovoltaic (OPV) device based on a carbazole-derived copolymer poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and N,N′-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) was fabricated by incorporating alcohol-soluble phosphate group-containing perylene diimide derivative (PDIP) as a cathode interfacial layer. The final performance of PDI-based OPV device modified by PDIP layer enhanced due to both optimized interfacial contact and the formation of interfacial dipole. Firstly, the film roughness of active layer was reduced from 8.8 nm to less than 4.0 nm by the introduction of the relatively amorphous PDIP layer. Meanwhile, the surface of active layer became more hydrophilic with significantly decreasing the contact angle from 90° to 78°. Secondly, an interfacial dipole between active layer and metal electrode was formed as indicated by the surface potential measurement, which not only enhanced built-in potential but also improved charge transport and extraction. Thus, the final improved device performance of PDI-based OPV device with simultaneous enhancement of open-circuit voltage (VOC) and short-circuit current density (JSC) was achieved.

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