Configuration Engineering of Unsymmetrical Structural Hole Transport Material for Efficient and Stable Regular/Inverted Perovskite Solar Cells

An effective hole transport material (HTM) should have the characteristics of high hole mobility, good film-forming property, and a well-matched energy level. In this work, we designed and synthesized two Y-shaped HTMs, in which the phenanthrol[9,10-d]imidazole group was integrated as the plane π building block into triphenylamine (TPA) or N3,N3,N6,N6-tetraphenyl-9H-carbazole-3,6-diamine (CZDPA) donors, cited as 2TPA-PI and p-CZDPA-PI, respectively. By adjustment of the incorporation of electron donors and the building block core, the film morphology, hole mobility, and energy band alignment are well manipulated. It is found that an unsymmetrical molecular conformation supports high glass-transition temperature and uniform thin films for both HTMs. Contrary to our expectations, p-CZDPA-PI with large conjugated CZDPA donors shows low hole mobility and up-shifted energy level compared to 2TPA-PI with propeller structural TPA donors. As a result, once utilized as an HTM, 2TPA-PI reveals a maximum efficiency of 17.58 and 20.32% in the inverted and regular perovskite solar cells (PSCs), respectively. Furthermore, it is also found that the energy level alignment is of importance for the HTMs in regular PSCs by comparison to that in inverted PSCs. This work provides an effective strategy for designing compressive HTMs performing well in both regular and inverted PSCs.