Tandem Organic Solar Cells: Nonfullerene Tandem Organic Solar Cells with High Open‐Circuit Voltage of 1.97 V (Adv. Mater. 44/2016)

Abstract

Non-fullerene tandem organic solar cells (OSCs) with a high open-circuit voltages of 1.97 V were successfully demonstrated, wherein P3HT:SF(DPPB)4 and PTB7-Th:IEIC BHJs are used as the front and back subcells in an inverted tandem structure. A dual-functional ICL is exploited in the configuration of MoO3/ultrathin Ag/poly[(9,9-bis(3-(N,Ndimethylamino)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylflorene)] (PFN), which not only promotes the quasi-ohmic-contact between the two subcells, but also allows the optical field distribution of each of the subcells to be adjusted by creating microcavities between the ICL and the electrodes. With all the components identified, we first investigated the photovoltaic performance of single-junction cells in an inverted device with the structure of ITO/ZnO/PFN/Active layer/MoO3/Ag. We used the bi-layered cathode interfacial layer that combines a sol?gel ZnO with a thin layer of PFN for improving the interfacial contact with high LUMO SF(DPPB)4. When the thickness of the Ag increases to 5 nm, the performance of the tandem cell is improved to a PCE of 6.05% with high open-circuit voltages of 1.94 V, current density of 6.31 mA cm-2, and FF of 0.49. Further increasing the Ag layer to 8?15 nm, the high open-circuit voltages of tandem devices becomes stabilized at the value of 1.97 V. The front cell exhibits a spectral response at most of the high-energy photons within the range of 300?650 nm and the EQE peak is close to 52%, while the back cell shows a broad EQE spectrum in the visible range with strong absorption of the low-energy photons.