The dual role of ozone-treated aluminum doped zinc oxide for CH3NH3PbI3 solar cells

We present perovskite solar cells using ozone-treated aluminum doped zinc oxide (AZO:O3) in the dual role: as a transparent electrode and as an electron transport layer (ETL). Aluminum doped zinc oxide (AZO) replaces the conventional FTO/TiO2(c)/TiO2(m) stack, considerably simplifying the fabrication process and reducing thermal budget. Photoelectron spectroscopy suggests that AZO is an effective ETL for perovskite (CH3NH3PbI3) thin films, with a large valence band offset and a small conduction band offset, but with a possible path for carrier recombination at the interface. We show that treating the surface of AZO with ozone gas (AZO:O3) improves the charge carrier extraction at the interface. Detailed characterization of the AZO:O3/CH3NH3PbI3 interface shows that ozone reduces the oxygen vacancies and de-dopes top 6–9 nm of the AZO surface. The gradient in doping induces an electric-field at the AZO surface which enhances the carrier extraction. AZO:O3/CH3NH3PbI3/spiro-OMeTAD/Au devices show champion JSC, VOC and η of 20.92 mA/cm2, 1.03 V and 10.5% respectively. Meanwhile, average short-circuit current density (JSC) has improved from 16.32 mA/cm2 (AZO) to 19.74 mA/cm2 (AZO:O3). This is attributed to the induced electric-field at AZO:O3 surface leading to an enhanced extraction of photo-generated charge carriers. Devices hysteresis is also much lower than previously reported results. [Display omitted] •Dual Electronic band structure of Aluminum doped-ZnO (AZO).•Effect of ozone-gas treatment on electronic band-diagram of AZO.•Improved charge extraction in ozone-gas treated AZO.