Enhancement of power conversion efficiency of P3HT : PCBM solar cell using solution processed Alq3 film as electron transport layer

Solution-processed thin films of tris(8-hydroxyquinoline)aluminum (Alq3) have been produced and examined as an electron transport layer in P3HT:PCBM bulk heterojunction organic solar cells. UV–Vis absorption, XRD, SEM and current density–voltage (J–V) measurements both in dark and under illumination have been carried out. Absorption spectra of the active layer show typical P3HT:PCBM absorption features with a maximum absorption peak around 500 nm and two vibronic shoulders around 550 and 600 nm which were attributed to the inter-chain stacking of P3HT. Furthermore, XRD measurements revealed that the co-solvent processed film shows better crystallinity than the mono-solvent film. On the other hand, SEM images show a clear pinholing effect in the DCB-processed film which may cause leakage current that reduces the fill factor and overall power conversion efficiency (PCE) of the organic solar cell (OSC). Alq3 absorption spectra show an absorption peak in the UV region, with an optical band gap of 2.83 eV. The incorporation of Alq3 films as an electron transport layer in ITO/PEDOT:PSS/P3HT:PCBM/Alq3/Al structure has resulted in a significant enhancement in the performance of the studied OSC devices. The use of mixed solvents of dichlorobenzene and chlorobenzene (DCB:DB) together with the inclusion of Alq3 layer has resulted in enhanced PCE which reached 3.92 %.