[Investigation on performance enhancement of bulk heterojunction organic solar cells]

Four organic solar cells with the different structures were fabricated. The structures are Device1 ITO/LiF/PEDOT: PSS/MEH-PPV/C60/Al, Device 2 ITO/PEDOT : PSS/MEH-PPV/C60/Al, Device 3 ITO/LiF/PEDOT : PSS/MEH-PPV : C60/C60/Al and Device 4 ITO/PEDOT : PSS/MEH-PPV : C60/C60/Al. Then we compared the current-voltage (I-V) characteristics of these devices and found that the insertion of a thin LiF layer between the ITO electrode and the PEDOT : PSS layer resulted in much improved device performance. The short-circuit current density (J(sc)) and fill factor (FF) of Device 1 were enhanced by 74% and 31%, respectively as compared to those of Device 2. The short-circuit current density (J(sc)) of Device 3 is about 1.4 times as large as that of Device 4. The increased solar cell performance mostly can be attributed to the fact that the hole transport to the anode can be effectively suppressed by a thin LiF layer, and the thin LiF layer between the ITO electrode and the PEDOT: PSS layer can form better interface properties. Hence, such change in structure of solar cells improves the performance of the organic solar cells effectively.