Tandem solar cells involving metal-halide perovskite subcells offer routes to power conversion efficiencies (PCEs) that exceed the single-junction limit; however, reported PCE values for tandems have ...so far lain below their potential due to inefficient photon harvesting. Here we increase the optical path length in perovskite films by preserving smooth morphology while increasing thickness using a method we term boosted solvent extraction. Carrier collection in these films - as made - is limited by an insufficient electron diffusion length; however, we further find that adding a Lewis base reduces the trap density and enhances the electron-diffusion length to 2.3 µm, enabling a 19% PCE for 1.63 eV semi-transparent perovskite cells having an average near-infrared transmittance of 85%. The perovskite top cell combined with solution-processed colloidal quantum dot:organic hybrid bottom cell leads to a PCE of 24%; while coupling the perovskite cell with a silicon bottom cell yields a PCE of 28.2%.
The energy level alignment of the perovskite and hole transporting materials (HTMs) is essential for increasing the open‐circuit voltage (Voc) and enhancing the performance of perovskite solar cells ...(PSCs). In this work, new sequentially fluorinated poly(triarylamine) polymers (PTAA, 1F‐PTAA, and 2F‐PTAA) with tuned highest occupied molecular orbital (HOMO) energy levels are developed and applied as HTMs into PSCs. The fluorination approach successfully leads to stepwise downshifting of the HOMO levels of PTAA derivatives, resulting in an obvious increase in the Voc and power conversion efficiency (PCE) of the PSCs. In particular, introduction of 1F‐PTAA polymer in (FAPbI3)0.85(MAPbBr3)0.15‐based mesoporous n‐i‐p structure PSCs achieves the high stabilized PCE of 21.2% at the maximum power point with improved Voc of 1.14 V. To elucidate the importance of the optimized degree of fluorination of PTAA polymers on the photovoltaic performances, the optical, electrical, photophysical properties, and doping behaviors of the fluorinated PTAA derivatives are investigated.
New polymeric hole transporting materials (HTMs) with downshifted highest occupied molecular orbital (HOMO) energy levels are developed by sequentially introducing electron‐withdrawing fluorine groups into triarylamine‐based polymers. High‐performance perovskite solar cells with these HTMs exhibit outstanding efficiency at maximum power point of 21.2% and high open‐circuit voltage of 1.14 V as a result of a deeper HOMO level and efficient charge extraction.
Perovskite solar cells typically comprise electron- and hole-transport materials deposited on each side of a perovskite active layer. So far, only two organic hole-transport materials have led to ...state-of-the-art performance in these solar cells
: poly(triarylamine) (PTAA)
and 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD)
. However, these materials have several drawbacks in terms of commercialization, including high cost
, the need for hygroscopic dopants that trigger degradation of the perovskite layer
and limitations in their deposition processes
. Poly(3-hexylthiophene) (P3HT) is an alternative hole-transport material with excellent optoelectronic properties
, low cost
and ease of fabrication
, but so far the efficiencies of perovskite solar cells using P3HT have reached only around 16 per cent
. Here we propose a device architecture for highly efficient perovskite solar cells that use P3HT as a hole-transport material without any dopants. A thin layer of wide-bandgap halide perovskite is formed on top of the narrow-bandgap light-absorbing layer by an in situ reaction of n-hexyl trimethyl ammonium bromide on the perovskite surface. Our device has a certified power conversion efficiency of 22.7 per cent with hysteresis of ±0.51 per cent; exhibits good stability at 85 per cent relative humidity without encapsulation; and upon encapsulation demonstrates long-term operational stability for 1,370 hours under 1-Sun illumination at room temperature, maintaining 95 per cent of the initial efficiency. We extend our platform to large-area modules (24.97 square centimetres)-which are fabricated using a scalable bar-coating method for the deposition of P3HT-and achieve a power conversion efficiency of 16.0 per cent. Realizing the potential of P3HT as a hole-transport material by using a wide-bandgap halide could be a valuable direction for perovskite solar-cell research.
The formation of a dense and uniform thin layer on the substrates is crucial for the fabrication of high-performance perovskite solar cells (PSCs) containing formamidinium with multiple cations and ...mixed halide anions. The concentration of defect states, which reduce a cell’s performance by decreasing the open-circuit voltage and short-circuit current density, needs to be as low as possible. We show that the introduction of additional iodide ions into the organic cation solution, which are used to form the perovskite layers through an intramolecular exchanging process, decreases the concentration of deep-level defects. The defect-engineered thin perovskite layers enable the fabrication of PSCs with a certified power conversion efficiency of 22.1% in small cells and 19.7% in 1-square-centimeter cells.
Halide perovskite solar cells (PSCs) have recently shown a leap forward in performance by reducing the recombination loss at the interface between the perovskite and hole-transporting layers through ...surface treatment. However, additional surface treatment processes such as spin-coating or annealing are undesirable for commercialization in terms of the production cost. In addition, commonly used organic hole-transporting materials (HTMs) such as 2,2′,7,7′-tetrakis
N
,
N
-di(4methoxylphenyl)amino-9,9′-spirobifluorene (spiro-OMeTAD) and poly(triarylamine) (PTAA) are used with hygroscopic additives, which deteriorate the long-term stability and hinder the commercialization of PSCs. Herein, we report an efficient strategy for interface engineering by directly incorporating gallium(
iii
) acetylacetonate (Ga(acac)
3
) into HTMs without subsequent processes and hygroscopic dopants. The incorporated Ga(acac)
3
spontaneously interacts with the surface of the perovskite layer, yielding a reduction of the interfacial recombination loss for various organic HTMs. In particular, by applying Ga(acac)
3
in poly(3-hexylthiophene) (P3HT), the PSCs showed a significant improvement in the power conversion efficiency (PCE) from 17.7% for the control device to 21.8%. The Ga(acac)
3
-devices also showed superior moisture stability for 2000 hours under 85% relative humidity at room temperature without any encapsulation, maintaining a complete initial performance. We also demonstrated that the incorporated Ga(acac)
3
successfully works on the best-known PSCs with the aligned P3HT, showing an enhanced PCE of 24.6%. We believe that this work presents a route for the high performance and commercialization of PSCs.
Halide perovskite solar cells (PSCs) have recently shown a leap forward in performance by reducing the recombination loss at the interface between the perovskite and hole-transporting layers through surface treatment.
Copolymers composed of diketopyrrolopyrrole and phenylene units with different numbers of fluorine subsitution are synthesized. When the effect of the number of fluorine substitution on the n‐channel ...transporting property is investigated, the polymer with four fluorine substitutions exhibits the best n‐type charge‐transporting behavior with an electron mobility of 2.36 cm2 V−1 s1.
Fluorination of conjugated polymers is one of the effective strategies to tune the frontier energy levels for achieving high efficiency polymer solar cells. In this study, three fluorinated D-A ...polymers, consisting of 3,3'-difluoro-2,2'-bithiophene and 2,1,3-benzothiadiazole (BT) with different numbers of fluorine substitution, were synthesized in order to investigate the effect of fluorination on their photovoltaic properties. The polymers with fluorinated BT show lower frontier energy levels, improved polymer ordering, and a narrower fibril size in the blend with PC sub(71)BM. The polymer with mono-fluorinated BT exhibits a superior PCE of 9.14% due to a high SCLC hole mobility, mixed orientation of polymer crystals in the active layer, and low bimolecular recombination. This result demonstrates that the fluorine content in conjugated polymers should be controlled for optimizing optoelectrical and photovoltaic properties of fluorinated conjugated polymers.
The open‐circuit voltage (Voc) of perovskite solar cells is limited by non‐radiative recombination at perovskite/carrier transport layer (CTL) interfaces. 2D perovskite post‐treatments offer a means ...to passivate the top interface; whereas, accessing and passivating the buried interface underneath the perovskite film requires new material synthesis strategies. It is posited that perovskite ink containing species that bind strongly to substrates can spontaneously form a passivating layer with the bottom CTL. The concept using organic spacer cations with rich NH2 groups is implemented, where readily available hydrogens have large binding affinity to under‐coordinated oxygens on the metal oxide substrate surface, inducing preferential crystallization of a thin 2D layer at the buried interface. The passivation effect of this 2D layer is examined using steady‐state and time‐resolved photoluminescence spectroscopy: the 2D interlayer suppresses non‐radiative recombination at the buried perovskite/CTL interface, leading to a 72% reduction in surface recombination velocity. This strategy enables a 65 mV increase in Voc for NiOx based p–i–n devices, and a 100 mV increase in Voc for SnO2‐based n–i–p devices. Inverted solar cells with 20.1% power conversion efficiency (PCE) for 1.70 eV and 22.9% PCE for 1.55 eV bandgap perovskites are demonstrated.
Interfacial nonradiative recombination limits the open‐circuit voltage of perovskite solar cells. A buried interface passivation strategy is developed that can be used across metal oxide transport layers. Perovskite precursors containing large organic cations with high affinity for the substrate spontaneously form a 2D passivation layer on the underlying metal oxides, which reduces interfacial recombination by 72%.
Abstract
Many of the best-performing perovskite photovoltaic devices make use of 2D/3D interfaces, which improve efficiency and stability – but it remains unclear how the conversion of 3D-to-2D ...perovskite occurs and how these interfaces are assembled. Here, we use in situ Grazing-Incidence Wide-Angle X-Ray Scattering to resolve 2D/3D interface formation during spin-coating. We observe progressive dimensional reduction from 3D to
n
= 3 → 2 → 1 when we expose (MAPbBr
3
)
0.05
(FAPbI
3
)
0.95
perovskites to vinylbenzylammonium ligand cations. Density functional theory simulations suggest ligands incorporate sequentially into the 3D lattice, driven by phenyl ring stacking, progressively bisecting the 3D perovskite into lower-dimensional fragments to form stable interfaces. Slowing the 2D/3D transformation with higher concentrations of antisolvent yields thinner 2D layers formed conformally onto 3D grains, improving carrier extraction and device efficiency (20% 3D-only, 22% 2D/3D). Controlling this progressive dimensional reduction has potential to further improve the performance of 2D/3D perovskite photovoltaics.
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