ABSTRACT
The continuing increase of the efficiency of perovskite solar cells has pushed the internal quantum efficiency approaching 100%, which means the light-to-carrier and then the following carrier transportation and extraction are no longer limiting factors in photoelectric conversion efficiency of perovskite solar cells. However, the optimal efficiency is still far lower than the Shockley-Queisser efficiency limit, especially for those inverted perovskite solar cells, indicating that a significant fraction of light does not transmit into the active perovskite layer to be absorbed there. Here, a planar inverted perovskite solar cell (ITO/PTAA/perovskite/PC61BM/bathocuproine (BCP)/Ag) is chosen as an example, and we show that its external quantum efficiency (EQE) can be significantly improved by simply texturing the poly[bis (4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) layer. By washing the film prepared from a mixed polymer solution of PTAA and polystyrene (PS), a textured PTAA/perovskite interface is introduced on the light-input side of perovskite to inhibit internal optical reflection. The reduction of optical loss by this simple texture method increases the EQE and then the photocurrent of the ITO/PTAA/perovskite/PC61BM/BCP/Ag device with the magnitude of about 10%. At the same time, this textured PTAA benefits the band edge absorption in this planar solar cell. The large increase of the short-circuit current together with the increase of fill factor pushes the efficiency of this inverted perovskite solar cell from 18.3% up to an efficiency over 20.8%. By using an antireflection coating on glass to let more light into the device, the efficiency is further improved to 21.6%, further demonstrating the importance of light management in perovskite solar cells.
ABSTRACT
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 60-80â 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.
ABSTRACT
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.
