Highly Efficient and Stable Perovskite Solar Cells Using a Dopant‐Free Inexpensive Small Molecule as the Hole‐Transporting Material

Abstract

The hole transporting layer (HTL) plays an important role in realizing efficient and stable perovskite solar cells (PSCs). In spite of intensive research efforts toward the development of HTL materials, low‐cost, dopant‐free hole transporting materials that lead to efficient and stable PSCs remain elusive. Herein, a simple polycyclic heteroaromatic hydrocarbon‐based small molecule, 2,5,9,12‐tetra(tert‐butyl)diacenaphtho[1,2‐b:1′,2′‐d]thiophenen, as an efficient HTL material in PSCs is presented. This molecule is easy to synthesize and inexpensive. It is hydrophobic and exhibits excellent film‐forming properties on perovskites. It has unusually high hole mobility and a desirable highest occupied molecular orbital energy level, making it an ideal HTL material. PSCs fabricated using both the n‐i‐p planar and mesoscopic architectures with this compound as the HTL show efficiencies as high as 15.59% and 18.17%, respectively, with minimal hysteresis and high long term stability under ambient conditions.

A structure–property study of fluoranthene-cored hole-transporting materials enables 19.3% efficiency in dopant-free perovskite solar cells

“…[42][43][44] Moreover, the unique central cyclopenta-fused ring endows the uoranthene with an electron-decient character, 45 which thereby can be used as an electron-withdrawing core to construct various D-A type HTMs. 46,47 Herein, we functionalize the uoranthene moiety with methoxy-substituted triphenylamine (TPA) units on the 3-, 8-positions or 3-, 8-, 9-positions to form a linear and star-shaped structure, respectively. In addition, the connection between the TPA units and the central uoranthene core (single bond vs. ethylene) as well as the substitution positions of methoxy groups in the TPA units (para-vs. meta-) are also tuned to elucidate how these structural variations affect HTM properties and the resultant performance in PVSCs.…”

Hole Transport Materials in Conventional Structural (n–i–p) Perovskite Solar Cells: From Past to the Future

“…Stability was also improved, and it retained over 60–70% of its original efficiency for 400 min under illumination at AM 1.5G because of the absence of dopants and hydrophobicity . A simple polycyclic, heteroaromatic, hydrocarbon‐based HTM, called PCA‐1 , has recently been developed (Figure ) . PCA‐1 did not require dopants to improve the hole mobility because that of PCA‐1 could be increased following thermal annealing (8.3 × 10 −5 → 8.3 × 10 −2 cm 2 V −1 s −1 ).…”

A Review on Solution‐Processable Dopant‐Free Small Molecules as Hole‐Transporting Materials for Efficient Perovskite Solar Cells

“…In parallel with these donor-acceptor type SM-HTMs, those with only donor units were also attractive. [153][154][155][156][157][158] In 2017, the carbazole-based SM-HTM reached its first PCE of over 15%, where Li et al [153] anchored three carbazole units on the phenol core, and the molecule TCP-OH presented a well-aligned HOMO level with the VBM level of perovskite to transfer the holes and a large bandgap (E g ) to afford a quite shallow LUMO level to efficiently block the photogenerated electrons. The corresponding PSC device delivered a PCE of 16.97% and a better long-term stability relative to the spiro-OMeTAD device due to the higher T g .…”

“…In 2018, Peng et al [154] fused two acenaphthene units with thiophene unit or naphthalene unit to produce molecules PCA-1 and PCA-2. The peripheral tert-butyl sidechains were designed to weaken the intermolecular π-π stacking, imparting a good solubility to the molecules as well as a smooth surface and amorphous nature to the HTLs.…”