Interfacial Engineering of P3HT/ZnO Hybrid Solar Cells by Phthalocyanines: a Joint Theoretical Experimental Investigation

The present work[1] combines atomistic simulations and experimental investigations to study heterojunction interfaces of hybrid polymer solar cells, with the aim to better understand and precisely predict their photovoltaic properties. A state-of-the-art theoretical multiscale approach rooted on ab initio calculations[2], has been used to model an original, hybrid ternary system based on a P3HT/Zinc Phthalocyanine (ZnPc)/ZnO interface[3,4], in which a ZnPc interlayer is applied to improve the performance of the hybrid interface. The theoretical findings have been then validated against the properties of concrete P3HT/ZnPc/ZnO planar heterojunction devices. Our theoretical predictions are in close agreement with the photovoltaic properties obtained in such a kind of P3HT/ZnPc/ZnO solar cells, indicating the strength of the present approach for modeling hybrid heterojunction interfaces. In detail, our jointly obtained theoretical and experimental results reveal that: (i) ZnPc molecules in direct contact with a ZnO surface insert new energy levels due to a strong ZnPc/ZnO coupling[3] (ii) electron injection from these new energy levels of ZnPc into ZnO is highly efficient, (iii) the ZnPc/ZnO coupling strongly influences the energy levels of the ZnO and P3HT leading to a reduction of the open circuit voltage, and (iv) charge carrier recombination at the P3HT/ZnO interface is reduced by the ZnPc interlayer. In practice, the intercalation of ZnPc leads to an increase in photocurrent as well as to an overall increase in power conversion of the planar hybrid heterojunction by 50%, thus stressing the importance of interfacial engineering in hybrid solar cells. This work was developed as a collaboration between CNR-ISM Montelibretti (RM), CNR-IOM Cagliari, and CNRS-CINaM (Marseille,France) within the IIT-SEED Project POLYPHEMO funded by Italian Institute of Technology. References [1] G. Mattioli, et al.; Adv. Energy Mater., (2014) 1301694, DOI: 10.1002/aenm.201301694 [2] C. Melis, et al.; ACS NANO, 5, (2011) 9639 [3] G. Mattioli, et al.; J. Phys. Chem. C, 116 (2012) 15439 [4] C. Melis, et al.; J. Phys. Chem. C, 115 (2011) 18208