Carbon nanotubes embedded poly(3,4-ethylenedioxythiophene):poly (styrenesulfonate) hybrid hole collector for inverted planar perovskite solar cells

This study presents a hybrid hole collector that consists of metallic single-walled carbon nanotubes (CNTs) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and is applicable in inverted planar perovskite solar cells. The drop-tasted CNTs exhibit superior optical transmission and hole extraction properties compared to conventional PEDOT:PSS; however, the inherent random networks of CNTs result in many vacancies between nanotubes, causing recombination losses when employed solely as a hole transport layer in the planar architecture of solar cells. Thus, the proposed hybrid hole collector is designed by blending CNTs with various mixture ratios (10-50%) of PEDOT:PSS to enhance the electron-blocking properties. The preferred CNT (70%)/PEDOT:PSS (30%) composition shows a dense, pinhole-free surface and better photoluminescence quenching properties than pristine PEDOT:PSS. After device fabrication, we demonstrate that this hybrid hole collector impressively enhanced average power conversion efficiency from 13.2% to 15.6% (up to 16.0% for best-performing cell) with negligible hysteresis. Time-correlated single-photon counting and conductive atomic force microscopy analyses elucidate the performance progress for the CNT/PEDOT:PSS composite in terms of better hole collection and highly conductive characteristics. This approach supports simple solution-processing techniques at low temperatures, which can construct promising routes for the development of inverted planar perovskite-based photovoltaics with reduced hygroscopic and acidic PEDOT:PSS content.