CoBr2-doping-induced efficiency improvement of CsPbBr3 planar perovskite solar cells

Abstract

Although perovskite solar cells (PSCs) have achieved the highest power conversion efficiency (PCE) of 25.2% in a very short period of development, they suffer from poor stability because the organic–inorganic hybrid perovskite materials are easily decomposed under the attacks of oxygen, moisture, heat and ultraviolet light. It is demonstrated that an all inorganic perovskite material of CsPbBr₃ has excellent stability against moisture, oxygen and heat, but it has a slightly wide bandgap of 2.3 eV, which seriously hinders light absorption and leads to poor PCE. Metal ion doping is a good approach to overcome this drawback because it can effectively tune the bandgap, enhance light absorption, suppress trap states and adjust the energy level. Here, we use the CoBr₂ doping route to fabricate high quality and crystallinity CoBr₂ doped CsPbBr₃ film. As a result, a champion device with the CsPb_0.998Co_0.002Br₃ film yields a PCE as high as 8.57%, much higher than that of the pristine CsPbBr₃ one (6.81%). It is found that the lower number of trap defects and higher carrier density of the CsPb_0.998Co_0.002Br₃ film are key reasons for the enhancement because they bring about better charge carrier dynamics and suppressed dark recombination.