Improved Stability of Perovskite Solar Cells with a Surface Treated Electron Transport Layer

Abstract

Perovskite devices have garnered a lot of attention due to their remarkable opto-electronic properties such as high absorption coefficient, high charge carrier mobility and lifetime and long charge- carrier diffusion length. Within a space of 10 years, their efficiencies have quickly risen from 3.8% to 22.1%. However perovskite devices are unstable when exposed to air therefore limiting their use in outdoor application. This effect is even more apparent in inverted planar heterojunction structured devicies with a p-i-n layout, which use poly (3,4-ethylenedioxythiophene)-poly (styrene sulfonate) PEDOT:PSS as a hole transport layer and [6,6]-phenyl-C61 -butyric acid methyl ester PCBM as an electron transport layer. Devices based on this structure are preferable because they are hysteresis free, low temperature processing and high device efficiency as well as potential for use in flexible devices. In this study, we determine the primary source of device failure in our devices and based on this concept, we develop a technique that enhances the device stability of P-I-N PSCs. By surface treatment of the PCBM layer with hydrophobic Stearic acid, we achieved increased moisture resistivity of PCBM. The treated surface of PCBM has improved hydrophobicity and consequently prevents water ingress in the perovskite layer longer compared to non-treated surfaces. Importantly, treated devices exhibited improved stability in their photovoltaic parameters compared to non-treated devices when exposed to an environment of relative humidity (RH) 40%.