Recent research in organic photovoltaic (OPV) is largely focused on developing low cost OPV materials such as graphene. However, graphene sheets (GSs) blended conjugated polymers are known to show inferior OPV characteristics as compared to fullerene adduct blended with conjugated polymer. Here, we demonstrate that graphene quantum dots blended with regioregular poly(3-hexylthiophene-2,5-diyl) or poly(2-methoxy-5-(2-ethylhexyloxy)-1,4phenylenevinylene) polymer results in a significant improvement in the OPV characteristics as compared to GSs blended conjugated polymers. This work has implications for inexpensive and efficient solar cells as well as organic light emitting diodes.

We demonstrate organic photovoltaic devices incorporating two donors, namely, copper phthalocyanine (CuPc) and boron sub-phthalocyanine chloride (Sub-Pc) in association with single acceptor fullerene (C60) with sensitivity extending across the visible solar spectrum. It has been found that the absorption in different spectral regions in CuPc and Sub-Pc results in efficient harvesting of incident light photons which leads to enhanced power conversion efficiency (η). An enhancement in η from 0.64%, in the device architecture indium-tin-oxide (ITO)/CuPc(20 nm)/C60(40 nm)/bathophenanthroline (BPhen) (8 nm)/Al(150 nm), to ∼1.3% in the optimized device having a 2 nm layer of Sub-Pc in the geometry ITO/CuPc(18 nm)/Sub-Pc(2 nm)/C60 (40 nm)/BPhen (8 nm)/Al(150 nm) has been observed. This enhancement in η is dominantly attributed to the increment in short circuit current density (Jsc) due to efficient photon harvesting by incorporation of dual donors.

We demonstrate the effect of temperature on the performance of a copper phthalocyanine (CuPc)/fullerene (C60) based bilayer organic photovoltaic device. The current–voltage (J–V) characteristics of the device have been studied in the dark as well as under illumination at different temperatures in the range 300–125 K. The variation in temperature strongly influences the device parameters and hence its performance. It has been found that (i) the lowering of the temperature results in a reduction in the rectification ratio, (ii) reverse bias current at low temperatures is governed by the tunnelling of the charge carriers and (iii) short circuit current (Jsc) decreases while the open circuit voltage (Voc) increases with the decrease in temperature. The change in Voc with temperature has been attributed to the variation in the built-in voltage (Vbi) arising due to band bending with a decrease in temperature. In summary the overall efficiency of the device first increases and then decreases with the reduction in temperature.

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