Enhanced Efficiency of n‑i‑p Perovskite Solar Cells and Defect Passivation Using a Triphenylamine-Based Hole Transporting Interfacial Layer

The
perovskite film surface and boundary defects are
said to constitute
nonradiative recombination and degradation sites, which limits the
potential for perovskite solar cells’ (PSCs) long-term stability
and power conversion efficiency (PCE). In order to overcome these
limitations, herein we introduce a low-cost triphenylamine-based dopant-free
molecule with a donor–acceptor–donor (D–A–D′)
type structure, namely “TPA-ThA”, as a
hole-transporting interfacial layer, which effectively passivates
the perovskite surface defects and adjusts the energy level alignment
between the perovskite/hole transport layer (spiro-OMeTAD). This passivator TPA-ThA, consisting of cyanopyridine as the acceptor core
moiety and thiophene and triphenylamine as the donor units, was obtained
by two-step synthetic methods without using the expensive catalyst
and characterized spectroscopically. Further, strong compatibility
with spiro-OMeTAD could result in the formation of a robust bilayer,
which decreased the ion migration from the perovskite and effectively
suppressed the moisture penetration toward the perovskite. Additionally,
it has been shown that a conjugated ring merging into the molecular
geometry is a useful method for enhancing the state of thermal stability,
hole mobility, and charge extraction capability. Because of the better
interface charge transfer/extraction and quality of perovskite films,
we achieved a PCE of 14.65%, a short-circuit current density of 18.72
mA/cm2, an open-circuit voltage of 1.062 V, and a fill
factor of 73.66% in the n-i-p structure composed of ITO/SnO2/perovskite/TPA-ThA/spiro-OMeTAD/Ag at the relative
humidity of 70 ± 10%. As a result, the findings offer a viable
approach to synthesize a hole-transporting interfacial layer compound
for effective and long-lasting PSCs.