Polymer and Nanocrystal Organizations in Polymer/inorganic Nanocrystal Hybrid Cells

In addition to fullerenes and their derivatives, semiconducting inorganic nanocrystals such as CdSe, ZnO, and [IMAGE png] nanoparticles/nanorods are also promising alternative electron acceptor material for BHJ OPVs. One primary feature of polymer/inorganic nanocrystal BHJ hybrid cells is the tunability of the nanocrystal shapes/sizes. By synthesizing nanocrystals in different shapes [e.g., nanoparticles (NPs), nanorods (NRs), and even nanotetrapods] with controllable sizes, the nanocrystal electronic properties can be manipulated to optimize device performance. Nanocrystal shapes/sizes have significant impacts on the polymer/nanocrystal organizations in the BHJ layer, which is critical for the solar cell performance. However, the correlations of polymer and nanocrystal organizations in polymer/inorganic nanocrystal BHJ hybrid cells are still unknown since their introduction in 2002. In this work, we developed a CG molecular simulation model to investigate polymer/nanocrystal organizations and morphological properties (e.g., specific interfacial area) in P3HT/[IMAGE png] NP/NR blends, see Fig. a. Our simulation system sizes were compatible with experiments (left panels in Fig. b), and the nanocrystal organizations in P3HT:[IMAGE png] NP/NR blends from our CGMD simulations (right panels in Fig. b) are in excellent agreements with those from electron tomography. Our simulation results indicate that anisotropic NRs can effectively promote polymer crystallinity because of preferential alignment of P3HT chains along the axial vectors of [IMAGE png] NRs; Figure c displays the degrees of P3HT chain alignment with NR axis as a function of distance from NR surface, and it is clear that P3HT chains close to NR surface prefer aligning with NR axial directions. Hence, in P3HT:[IMAGE png] NR blends NRs provide templates for P3HT crystallization, which is displayed schematically in Fig. d. Furthermore, our CGMD simulations also indicated that for NPs/NRs with similar diameters, NRs can effectively eliminate inter-nanocrystal junctions, thereby promoting electron transport. Therefore, the present study provides comprehensive insights into the correlations of polymer/nanocrystal organizations in polymer/inorganic nanocrystal hybrid solar cells, which is potentially helpful for nanomorphology control in next generation polymer/inorganic nanocrystal solar cells or thin film transistors. This project was in collaboration with Prof. Chun-Wei Chen at National Taiwan University, and the results of this work have been published in the Energy [IMAGE png] Environmental Science (DOI:10.1039/C2EE23372J) and the Journal of Physical Chemistry C (DOI:10.1021/jp306921e).

Figure: (a) CG models for P3HT chains and [IMAGE png] nano crystals. (b) BHJ nanomorphologies of P3HT:[IMAGE png] NP (upper panels) and NR (lower panels) from CGMD simulations; P3HT and [IMAGE png] nanocrystals are colored in red and blue, respectively. (c) degree of axial alignment of P3HT chains with axial vectors of [IMAGE png] NRs as the function of distance from NR surface. (e) schematics of P3HT crystallization along [IMAGE png] NR axis.