Molecular Engineering of Star‐Shaped Indoline Hole Transport Materials: The Influence of Planarity on the Hole Extraction and Transport Processes

Abstract

As the key properties of perovskite solar cells (PSCs), the hole extraction and transport capabilities of the hole transport material (HTM) affect the photovoltaic performance of PSCs to a considerable extent, while both capabilities can be adjusted by molecular planarity. Therefore, in this work, the molecular planarity of the HTM is systematically optimized to regulate the hole extraction and transport capabilities. Along with the improvement in planarity, the HTM′s HOMO level is increased, leading to the enhancement of hole extraction capability. Meanwhile, the hole transport capability can also be improved due to the intensification of molecular stacking during the film formation. As a result, the planar HTM achieves a relatively high efficiency of 18.48 %, which is higher than that of spiro‐OMeTAD. Accordingly, the molecular planarity presents an important impact on the photovoltaic performance of PSCs, providing us with a promising strategy for further optimization of efficient HTMs.

Backbone Engineering Enables Highly Efficient Polymer Hole‐Transporting Materials for Inverted Perovskite Solar Cells

“…The front-view images of the geometrically optimized molecular structures in Figure S18, Supporting Information, further verifies the conclusion aforementioned, indicating that the optimized structure of PTAA-P1,2 may be beneficial to the charge transfer at the interface. [58,59] Moreover, to quantitatively compare the regularity of these three polymer HTMs, the vertical distances between the N atoms in the backbones of polymers and the (100) plane of perovskite bottom surface are calculated (see inset of Figure 2d), which are defined as the N-to-(100) plane vertical distances. As portrayed in Figure 2d, PTAA and PTAA-P2 both exhibit broad distribution of N-to-(100) plane vertical distances from 4 to 12 Å.…”

“…The front‐view images of the geometrically optimized molecular structures in Figure S18, Supporting Information, further verifies the conclusion aforementioned, indicating that the optimized structure of PTAA‐P1,2 may be beneficial to the charge transfer at the interface. [ 58,59 ]…”