Photoinduced Self-Gating of Perovskite Photovoltaic Cells in Ionic Liquid

Abstract

We demonstrate that the power conversion efficiency (PCE), photocurrent, and fill factor (FF) of perovskite solar cells (PSC) can be significantly improved by the photoinduced self-gating in ionic liquids (ILs) via n-doping of the carbon nanotube (CNT) top electrode on the fullerene electron transport layer (ETL). CNTs, graphene, and other carbon electrodes have been proven to be stable electrodes for PSC, but efficiency was not high. We have previously shown that the performance of PSCs with CNT electrodes can be improved by IL gating with gate voltage (V g ) applied from an external power source. Here we demonstrate that effective self-gating in ILs is possible by a photoinduced process, without an external source. The open circuit voltage (V oc ) generated by the PSC itself can be applied to the CNT/C60 electrode as V g leading to photogating. This self-gating with V oc is compared to photocharging of CNTs in ILs without any gating for two types of fullerene ETLs: C 60 and C 70 , Two types of ILs, DEME-TFSI and BMIM-BF 4 , are tested for two types of nanotubes electrodes: single wall (SWCNT), and multiwall (MWCNT). The resulting improvements are analyzed using the effective diode-circuit (DC) and the drift-diffusion (DD) models. Self-gating allows the PCE improvement from 3−5% to 10−11% for PSCs with a thick ETL, while for optimal combination of a thin SWCNT/ETL with added layers for improved stability, the PCE reached 13.2% in DEME-TFSI IL.

Temperature Dependence of Photoinduced Phase Segregation in Bromide-Rich Mixed Halide Perovskites

“…Since 2009, hybrid perovskites have proven to be an excellent material for optoelectronics, including solar cells (SCs), − light-emitting diodes (LEDs), − and various other device types. − Additionally, the perovskite bandgap can be continuously tuned by incorporating different halides into its structure. By introducing chloride, bromide, and iodide in different proportions to the perovskite composition, the bandgap can be adjusted within the range of 1.5–3.2 eV .…”