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Morphology and Molecular Packing in Polymer-Nanocrystal Hybrid Solar Cells Revealed with Synchrotron X-ray Characterization and Other Techniques

Final Report Summary - HYBRIDSOLAR (Morphology and Molecular Packing in Polymer-Nanocrystal Hybrid Solar Cells Revealed with Synchrotron X-ray Characterization and Other Techniques)

HYBRIDSOLAR aims to improve the understanding and performance of nontoxic, abundant nanocrystal solar cells through the completion of the project objectives: to control packing and morphology, correlate packing with material properties and solar-cell performance, correlate morphology with material properties and solar-cell performance, and use the improved understanding of molecular packing and morphology to make improved hybrid solar cells. Each of these objectives has been achieved, resulting in efficient solar cells made of nontoxic, abundant nanocrystals. The completion of each objective is described below. The only major modification to the project proposal is the use of AgBiS2 nanoparticles developed by our research group in place of the proposed Bi2S3 nanoparticles; this substitution was made due to the significant promise of AgBiS2 nanocrystals and has paid off as evidenced by the high efficiencies achieved with this material.

The packing and morphology of both the AgBiS2 nanocrystals and the polymer hole transport layer were controlled by varying processing conditions such as the annealing, the solvent, the solution concentration, and the ligand-exchange process, thus completing Objective 1. The morphology and packing of the materials were probed with a variety of techniques including UV-vis spectroscopy, x-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), small-angle X-ray scattering (SAXS), and wide-angle x-ray scattering (WAXS). These measurements were performed onsite at ICFO, in collaborator’s labs, or at either the ALBA synchrotron lightsource or the European Synchrotron Radiation Facility (ESRF). In order to complete Objectives 2 and 3, the measurement results were correlated with solar-cell performance, as indicated measurements of current-voltage (I-V) curves, external quantum efficiency (EQE), transient photovoltage (TPV), transient photocurrent (TPC), and Suns open-circuit voltage (Suns-Voc).

The understanding gained from the activities described above enabled us to improve the design of our solar cells and thereby achieve impressive efficiencies and fulfill Objective 4. Although solar-cell efficiencies were below 1% at the beginning of this project, our efforts have resulted in efficiencies up to 6.3%. To our knowledge, this represents the highest efficiency of any nontoxic nanoparticle solar cells that are solution processed at low temperatures. Our main results have been included in a patent application and a manuscript that is currently under review.