Efficient Generation of the Morphology of Organic Bulk Heterojunction Solar Cells Based on the Scanning Transmission X-Ray Microscopy Images

In organic bulk heterojunction (BHJ) solar cells, the morphology of the donor/acceptor (D/A) blend can significantly impact the charge generation efficiency and recombination losses, thus largely determining the device efficiency. In order to simulate the electronic processes in the working devices, near-exact reproduction of the morphology is very important but the method is still lacking. Here we developed an efficient way to reconstruct the morphologies of the DR3:OIDTBR solar cells under different annealing times by employing the 2 dimensional maps of the compositions (D/A percentage) along the thickness (z-) direction obtained by the Scanning Transmission X-ray Microscopy (STXM) technique. Considering the normalized pixel values in the STXM images as the probabilities for obtaining acceptor sites, the site types along each z-direction column in a 3-d cubic lattice are individually generated, and the same-type adjacent domains are merged to form larger domains. Then the Kawasaki-algorithm is applied to the morphology to smooth it and add lateral correlations to the domains. The average size, anisotropy and tortuosity of the domains are calculated and analyzed. The generated morphologies are further used for Kinetic Monte Carlo simulations of the internal quantum efficiencies, which are found to increase with the annealing time, being consistent with the experimental results. Our method provides an easy-to-implement and efficient mean to obtain a massive esemble of device morphology relative to the expensive ones like electron tomography, which can be used for simulating electronic properties of BHJ solar cells.