Efficient and Stable Planar n-i-p Perovskite Solar Cells with Negligible Hysteresis through Solution-Processed Cu2 O Nanocubes as a Low-Cost Hole-Transport Material.

Organic-inorganic halide perovskite solar cells (PSCs) have reached certified efficiencies of over 23 % with expensive organic hole-transporting materials. However, the use of an inorganic hole-transport layer (HTL) remains crucial as it would reduce cost combined with higher mobility and stability. In this direction, the application of Cu2 O as the top layer in PSCs is still complicated owing to the difficulty of solution processing. Herein, a solution-processing method is reported for preparing Cu2 O nanocubes as a p-type HTL in regular structure (n-i-p) PSCs. The controlled synthesis of Cu2 O nanocubes in a size range of 60-80 nm is achieved without using any surfactants, which are usually toxic and tricky to remove. The new structure of these Cu2 O nanocubes enhances the carrier mobility with preferable energy alignment to the perovskite layer and superb stability. The PSCs based on these Cu2 O nanocubes HTMs could achieve an efficiency exceeding 17 % with high stability, whereas organic P3HT-based PSCs display an efficiency of 15.59 % with a poorer running stability. This indicates that Cu2 O nanocubes are a promising HTM for efficient and stable PSCs.

High Open-Circuit Voltage of 1.134 V for Inverted Planar Perovskite Solar Cells with Sodium Citrate-Doped PEDOT:PSS as a Hole Transport Layer.

Poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS) plays an important role in inverted planar perovskite solar cells (IPPSCs) as an efficient hole extraction and transfer layer (HTL). The IPPSCs based on PEDOT:PSS normally display inferior performance with a reduced open-circuit voltage. To address this problem, here sodium citrate-doped PEDOT:PSS is adopted as an effective HTL for improving the performance of IPPSCs. Sodium citrate-doped PEDOT:PSS HTL improves the conversion efficiency of IPPSCs from 15.05% of reference cells to 18.39%. The large increase of the open-circuit voltage ( VOC) from 1.057 to 1.134 V is the main source for this performance enhancement. With the help of characterization analysis of ultraviolet photoelectron spectroscopy, scanning electron microscopy, electrochemical impedance spectroscopy, etc., the higher work function of the doped PEDOT:PSS film and the uniform crystallinity of the perovskite film on it are disclosed as the reasons for the increased VOC and the consequent performance enhancement.