The Central Role of Ligand Conjugation for Properties of Coordination Complexes as Hole-Transport Materials in Perovskite Solar Cells

Abstract

Two zinc-based coordination complexes Y3 and Y4 have been synthesized and characterized, and their performance as hole-transport materials (HTMs) for perovskite solar cells (PSCs) has been investigated. The complex Y3 contains two separate ligands, and the molecular structure can be seen as a disconnected porphyrin ring. On the other hand, Y4 consists of a porphyrin core and therefore is a more extended conjugated system as compared to Y3. The optical and redox properties of the two different molecular complexes are comparable. However, the hole mobility and conductivity of Y4 as macroscopic material are remarkably higher than that of Y3. Furthermore, when employed as hole-transport materials in perovskite solar cells, cells containing Y4 show a power conversion efficiency (PCE) of 16.05%, comparable to the Spiro-OMeTAD-based solar cells with an efficiency around 17.08%. In contrast, solar cells based on Y3 show a negligible efficiency of about 0.01%. The difference in performance of Y3 and Y4 is analyzed and can be attributed to the difference in packing of the nonplanar and planar building blocks in the corresponding materials.

Organic Salts as p-Type Dopants for Efficient LiTFSI-Free Perovskite Solar Cells

“…As shown in Figure a, the bare perovskite film surface shows a well-crystallized material with typical crystallite sizes of around 200–500 nm . After being coated with the reference HTL (Figure b), the perovskite surface is effectively coated, and the top surface is flat without visible pin holes.…”

“…As shown in Figure 4 a, the bare perovskite film surface shows a well-crystallized material with typical crystallite sizes of around 200–500 nm. 22 After being coated with the reference HTL ( Figure 4 b), the perovskite surface is effectively coated, and the top surface is flat without visible pin holes. Replacing the dopant FK209 with (MeO-TPD)TFSI has no obvious influence on the film quality, as indicated in Figure 4 c to 4 g, where different doping levels of up to a 40% molar ratio were investigated.…”

The evolution of triphenylamine hole transport materials for efficient perovskite solar cells

“…It is noteworthy that the conductivity of the more planar, conjugated molecule Y4 is remarkably higher than that of Y3. 133 As discussed in Section 2.5.2, an increased hole mobility of 1.0 Â 10 À3 cm 2 V À1 s À1 was reported for the sulfur-rich, organic HTM SMe-TATPyr. Interestingly, studies of this system revealed that the employment of an interfacial layer increased the PCE of SMe-TATPyr-treated perovskite solar cells from 20.4% to 22.3%.…”

“…The difference in the crystal packing of the non-planar vs. planar components in the two compounds is attributed to their different device properties. 133 A 5,10,15,20-tetrakis(4-[N,N-di(4-methoxyphenyl)amino phenyl])porphyrin was successfully prepared on a gram scale via the direct condensation of pyrrole and 4-[bis(4-methoxyphenyl)amino]benzaldehyde (Fig. 34a).…”

Thermally StableD2hSymmetric Donor‐π‐Donor Porphyrins as Hole‐Transporting Materials for Perovskite Solar Cells

“…also demonstrated that PSCs with a mixture of Co II and Co III ‐based porphyrins as HTM could achieve an efficiency of 20.5 % with improved thermal stability [37] . Recent advances in HTMs based on porphyrin in high‐performance PSCs are summarized in Table S1 [38–47] …”