Short talk-Degradation studies on DBP-C70 based organic solar cells by means of sensitive external quantum efficiency (sEQE) measurements

Organic photovoltaic (OPV) devices based on donor-acceptor heterojunctions have become an emerging competitive technology due to their advantages of low cost, flexibility, lightweight and high-throughput roll-to-roll production. However, achieving long-term stability of organic solar cells is a remaining bottleneck for the commercialization of this appealing technology. Detection of changes in the device parameters provides a deeper insight into the degradation mechanisms of the devices, which paves the way for strategies on device lifetime improvement.
Interfaces and morphology of donor (D) and acceptor (A) materials have an important impact on the stability of the organic devices. Residing at the D-A interface, charge transfer (CT) states represent the intermediate states between exciton dissociation and recombination, and play a crucial role for the performance of the devices. In the work presented here, we study the CT states in DBP-C70 based organic solar cells in inverted [1] and standard [2] architectures using sensitive external quantum efficiency (sEQE) measurements [3]. Our investigations suggest a morphological sensitivity at the D-A interface, which depends on the deposition sequence, here investigated amongst others by means of atomic force microscopy studies. Further, we utilize this technique to detect the probable morphological changes induced by various ISOS aging test conditions. The results propose that the decay behavior in these small molecule bilayer solar cells is less related to the changes at the D-A interface, suggesting a pronounced morphological stability, and instead most probably dominated by changes at the metal/organic interfaces in the devices.