4-tert-butylpyridine free hole transport materials for efficient perovskite solar cells: a new strategy to enhance the environmental and thermal stability

Organic semiconductors as hole transport materials (HTMs) often require additives, such as LiTFSI and tert-butylpyridine (TBP), in order to enhance their hole conductivities. However, the combination of lithium salts and TBP leads to significant HTM morphological deformation and poor device stability. Here we have successfully applied tetrabutylammonium (TBA) salts to replace both LiTFSI and TBP. A high power conversion efficiency of 18.4% has been achieved for the devices with TBATFSI, which is higher than the control devices with LiTFSI and TBP (18.1%). We also found that the anions in the TBA salts play important roles in the hole conductivity and uniformity of the HTM layer, as well as the hysteresis of the devices. More importantly, the devices with TBATFSI and TBAPF ₆ demonstrated significantly enhanced environmental and thermal stability. This new strategy of using TBA salts is promising for developing stable organic HTM thin films for solar cell applications.