Stability and efficiency improved perovskite solar cells through tuning the hydrophobicity of the hole transport layer with an organic semiconductor

Abstract

Researching planar heterojunction perovskite solar cells has become increasingly popular in view of pursuing both a better photovoltaic performance and enhanced environmental stability. Recently, the use of integrated hole transport layers (HTLs) has attracted much attention because of the improvements in power conversion efficiencies (PCEs). However, previous research studies usually focused on the HTLs in regular-type devices, which do not affect the formation of perovskite crystals. Here, we developed the HTL for inverted solar cells, which integrated organic poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b]-dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl] (PTB7) with poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). PTB7 is used to tune the energy alignment and hydrophobicity of PEDOT:PSS to improve the hole transportation and perovskite formation. The integrated HTL (PEDOT:PSS/PTB7) demonstrated an enhanced hole extraction performance in perovskite solar cells due to better matched energy alignment. Furthermore, the hydrophobic nature of PTB7 provides a non-wetting surface that is beneficial to the crystal formation of perovskite, resulting in higher quality perovskite crystals. Using this simple process, the developed group exhibited a PCE of 18.43%, which was 16.5% higher than that of the reference devices (15.82%). In addition, due to the moisture-blocking characteristics of PTB7, the long-term stability of the devices was also obviously enhanced under ambient air conditions (25 °C) without encapsulation.