Coordinated Optical Matching of a Texture Interface Made from Demixing Blended Polymers for High-Performance Inverted Perovskite Solar Cells

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.