Inverted Poly(3-hexylthiophene-2,5-diyl)(P3HT):[6,6]-Phenyl C61 butyric acid methyl ester (PCBM) bulk heterojunction solar cells with cadmium sulfide (CdS) as the hole blocking layer

Abstract

P3HT:PCBM bulk heterojunction solar cells with poly 3,4- ethylenedioxythiophene:poly styrenesulfonate (PEDOT: PSS) as Hole Blocking Layer (HBL) has become increasingly feasible with large-area of donor–acceptor interface for efficient light-induced charge separation. Few metal oxides have also been utilized for P3HT: PCBM based solar cells as HBL which blocks the back electron leakage and increasing the charge collection before recombining. Although PEDOT: PSS has been heavily studied in these types of solar cells, it has been identified as a source for degrading the active layer due to its hydrophobic nature. In this study, inverted P3HT: PCBM solar cells were fabricated by using either of CdS and TiO2 thin films as HBL, and the effects of CdS layer thickness on the device performance were investigated. The device with thin CdS layer offered short circuit (JSC) over 7.5 mA/cm2with an open circuit voltage (VOC) of 0.57 V which provides overall power conversion efficiency of over 2 % under AM 1.5 illumination (100 mW/cm2 ) conditions, which is over 100 % higher than that of Titanium dioxide thin film as the hole blocking layer. The major contribution is 75 % improvement in the VOC, due to the lower work function of CdS. Even though there was a small improvement in the VOC with the thickness of CdS thin film, the conversion efficiency is decreased due to reduced JSC as per the strong absorption of CdS in the UV region verified by the optical absorption spectra.