Dopant-free small molecule hole transport materials based on triphenylamine derivatives for perovskite solar cells

In the past decade, perovskite solar cells have become a promising candidate in the photovoltaic industry owing to their high power conversion efficiency that surpasses 25%. However, there are certain limitations that have hindered the development and full-scale practical application of these cells, including the high cost and degradation of perovskite caused by the dopants. Hence, there is an urgent need to develop dopant-free hole transport materials (HTMs). In recent years, HTMs based on triphenylamine (TPA-HTMs) are receiving growing interest owing to their high hole mobility, excellent film formation, and suitable energy levels. The literature here covers work relevant to TPA-HTMs in the last five years. They have been classified according to different core types. The correlations between performance and structure are summarized, and the future development trend of TPA-HTMs is highlighted.