Charge transfer modification of inverted planar perovskite solar cells by NiO_x/Sr:NiO_x bilayer hole transport layer

Perovskite solar cells (PSCs) are the most promising commercial photoelectric conversion technology in the future. The planar p-i-n structure cells have advantages in negligible hysteresis, low temperature preparation and excellent stability. However, for inverted planar PSCs, the non-radiative recombination at the interface is an important reason that impedes the charge transfer and improvement of power conversion efficiency. Having a homogeneous, compact, and energy-level-matched charge transport layer is the key to reducing non-radiative recombination. In our study, NiO_x/Sr:NiO_x bilayer hole transport layer (HTL) improves the holes transmission of NiO_x based HTL, reduces the recombination in the interface between perovskite and HTL layer and improves the device performance. The bilayer HTL enhances the hole transfer by forming a driving force of an electric field and further improves J_\rm sc. As a result, the device has a power conversion efficiency of 18.44%, a short circuit current density of 22.81 mA\cdotcm^-2 and a fill factor of 0.80. Compared to the pristine PSCs, there are certain improvements of optical parameters. This method provides a new idea for the future design of novel hole transport layers and the development of high-performance solar cells.