Low temperature processed ITO-free perovskite solar cells without a hole transport layer

Perovskite solar cells (PSCs) have been considered as a promising photovoltaic technology due to their attractive power conversion efficiency (PCE) exceeding 20% and ease of processability at low temperature. However, there have been a few reports on low temperature processed ITO-free PSCs. In this work, highly transparent and conductive poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (HC-PEDOT:PSS, PH1000) was employed as electrode as an alternative material to ITO. PSCs built on three different electrodes (PH1000-5%, PH1000-10% and PH1000-H) with or without a hole transport layer (HTL) were fabricated. The factors that influence the performance of PSCs such as conductivity, morphology, work function and wettability of the electrode, morphology of perovskite films and different electrode treatments were investigated. A comparison of different electrodes as well as their corresponding impact on the device performance were also presented. The optimized average PCE of 7.95% with the highest PCE up to 9.65% for PSCs built on the PH1000-10% electrode without HTL were achieved. When a layer of PEDOT: PSS was spin coated on PH1000-H to prevent perovskite from decomposing, the optimized PCE of 6.98% with the highest up to 9.31% was achieved. Our results indicate that PH-1000 is a promising material to replace both ITO electrode and HTL, providing a much simpler architecture for flexible PSC applications.