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.

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 Cu2O 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 Cu2O nanocubes as a p‐type HTL in regular structure (n‐i‐p) PSCs. The controlled synthesis of Cu2O 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 Cu2O nanocubes enhances the carrier mobility with preferable energy alignment to the perovskite layer and superb stability. The PSCs based on these Cu2O 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 Cu2O nanocubes are a promising HTM for efficient and stable PSCs.

Recently, Sn–Pb low‐bandgap (Eg) perovskite solar cells (PSCs) have attracted enormous interest as an ideal bottom cell for all‐perovskite tandem solar cells. However, due to the lack of high‐performance Sn–Pb low‐Eg PSCs, the development of all‐perovskite tandem solar cells is severely constrained. Herein, the performance of Sn–Pb low‐Eg (1.2 eV) PSC is improved significantly using diluted poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a hole transport layer with a maximum power conversion efficiency (PCE) up to 19.58% and short‐circuit current density of 29.81 mA cm−2. The four‐terminal (4‐T) all‐perovskite tandem solar cell is constructed using an optical splitting system with this high‐efficient low‐Eg PSC as the bottom cell and a wide‐Eg (1.6 eV) PSC as the top cell. The best all‐perovskite 4‐T tandem solar cell shows a PCE of 23.26%.

Nickel oxide (NiOx) as a hole transport layer has been vastly investigated in perovskite solar cells (PSCs) due to the nature of p-type doping, high transparent materials, and deep-lying valence...