Unraveling the High Open Circuit Voltage and High Performance of Integrated Perovskite/Organic Bulk-Heterojunction Solar Cells.

Abstract

We have demonstrated high-performance integrated perovskite/bulk-heterojunction (BHJ) solar cells due to the low carrier recombination velocity, high open circuit voltage (V_OC), and increased light absorption ability in near-infrared (NIR) region of integrated devices. In particular, we find that the V_OC of the integrated devices is dominated by (or pinned to) the perovskite cells, not the organic photovoltaic cells. A Quasi-Fermi Level Pinning Model was proposed to understand the working mechanism and the origin of the V_OC of the integrated perovskite/BHJ solar cell, which following that of the perovskite solar cell and is much higher than that of the low bandgap polymer based organic BHJ solar cell. Evidence for the model was enhanced by examining the charge carrier behavior and photovoltaic behavior of the integrated devices under illumination of monochromatic light-emitting diodes at different characteristic wavelength. This finding shall pave an interesting possibility for integrated photovoltaic devices to harvest low energy photons in NIR region and further improve the current density without sacrificing V_OC, thus providing new opportunities and significant implications for future industry applications of this kind of integrated solar cells.