Electrical and photovoltaic response of bulk hetero-junction device made from poly (3-phenyl azo methine thiophene) (PPAT) and 1, 1′-diallyl substituted 4, 4′-dipyridine (DADP)

Electrical and photovoltaic properties of donor–acceptor composite system comprised of poly (3-phenyl azo methine thiophene) (PPAT) and 1, 1′–diallyl substituted 4, 4′-dipyridine (DADP) were investigated. A significant enhancement of photocurrent was observed when PPAT was blended with DADP. The increase in photocurrent has been explained in terms of efficient charge separation that resulted from the transfer of photo-excited electrons from PPAT to DADP. The strong quenching of fluorescence of PPAT was caused by the presence of DADP that indicates the photo-induced charge transfer from PPAT to DADP. The open circuit voltage (Voc) generated in the device is independent of the variation of work function of negative metal electrode that has been explained in terms of Fermi level pinning between DADP and metal via surface charges. The electrical characteristics of ITO/PPAT: DADP/Al photovoltaic device were determined by analyzing the dependence of short circuit photocurrent density (Jsc) and Voc under illumination at different temperatures. The Voc decreases almost linearly with increasing temperature, while short-circuit photocurrent increases logarithmically with temperature and saturates at higher temperature above 330 K. This dependence of Jsc and Voc on temperature has been discussed in terms of possible mechanism that involves the photovoltage generation and charge carrier transport in the device under thermally activated state. The photovoltaic device made from PPAT: DADP blend has shown three times higher photosensitivity than that of made from pure PPAT.