A new method to improve the lifetime stability of small molecule bilayer heterojunction organic solar cells

Unencapsulated small molecular solar cells with a layer of carboxylated copper phthalocyanine (CuPc⁎) introduced between the donor copper phthalocyanine (CuPc) and acceptor 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDI), and using ITO and Ag as the cathode and anode were investigated for 35 days. The performance and stability were compared between traditional ITO/PEDOT:PSS/CuPc/PTCDI/Ag cells and the new ITO/PEDOT:PSS/CuPc/CuPc*/PTCDI/Ag cells. The comparison shows that the modified cell has an enhanced stability compared to traditional cells. The improvement of the lifetime is likely due to the CuPc* layer working as buffer layer to prevent humidity and oxygen from diffusing into the active layer. Different thicknesses of CuPc were investigated to study the effects of CuPc layer thickness on the electrical properties of these devices. It was found that the properties of the cell with 20 nm thickness of CuPc were the best.

► We added an additional layer to small molecule organic solar cells to improve stability.
► Stability was monitored over 35 days.
► Carboxylated copper phthalocyanine (CuPc*) improved device stability in air.
► Improvement was attributed to hydrophilic functional groups of the CuPc*.