Improved Efficiency of Perovskite Solar Cells with Low-Temperature-Processed Carbon by Introduction of a Doping-Free Polymeric Hole Conductor

Low-temperature-processed carbon-based perovskite solar cells (C-PSCs) are promising photovoltaic devices, because of their good stability, low cost, and simple preparation methods, which allow for scalable processing. Herein, C-PSCs with the n-i-p structure are prepared, using a SnO2 nanoparticles film as the electron-selective contact, MAPbI(3) perovskite as the intrinsic absorber layer (MA = methylammonium), and a carbon layer as the hole-selective layer and conductor. Carbon is, however, not an ideal hole-selective layer and it is found that improved solar cell performance can be obtained by introducing a polymeric hole conductor between the perovskite and the carbon layer. Specifically, undoped poly(3-hexylthiophene) (P3HT) is used for this purpose, as it is stable and highly hydrophobic. For ITO/SnO2/MAPbI(3)/carbon devices, a solar cell efficiency of up to 12.8% is obtained, increasing up to 15.7% with the inclusion of a P3HT layer, which increases open-circuit potential, photocurrent, and fill factor (FF). In comparison, ITO/SnO2/MAPbI(3)/P3HT/Au devices performed rather poorly (up to 11.7%). Encouraging stability is obtained for unencapsulated C-PSC devices: P3HT/carbon devices do not show any degradation in solar cell performance upon storage for 1 month in low humidity, while they maintain 70% of their initial efficiency after 900 h at 82 degrees C in air