Solution-induced morphology change of organic-inorganic hybrid perovskite films for high efficiency inverted planar heterojunction solar cells

Photo-Cross-Linked Fullerene-Based Hole Transport Material for Moisture-Resistant Regular Fullerene Sandwich Perovskite Solar Cells

Despite the high efficiencies currently achieved with perovskite solar cells (PSCs), the need to develop stable devices, particularly in humid conditions, still remains. This study presents the synthesis of a novel photo-cross-linkable fullerene-based hole transport material named FT12. For the first time, the photo-cross-linking process is applied to PSCs, resulting in the preparation of photo-cross-linked FT12 (PCL FT12). Regular PSCs based on C60-sandwich architectures were fabricated using FT12 and PCL FT12 as dopant-free hole transport layers (HTLs) and compared to the reference spiro-OMeTAD. The photovoltaic results demonstrate that both FT12 and PCL FT12 significantly outperform pristine spiro-OMeTAD regarding device performance and stability. The comparison between devices based on FT12 and PCL FT12 demonstrates that the photo-cross-linking process enhances device efficiency. This improvement is primarily attributed to enhanced charge extraction, partial oxidation of the HTL, increased hole mobility, and improved layer morphology. PCL FT12-based devices exhibit improved stability compared to FT12 devices, primarily due to the superior moisture resistance achieved through photo-cross-linking.

Influence of Film Quality on Power Conversion Efficiency in Perovskite Solar Cells

Abstract: Organic-inorganic perovskite solar cells (PSCs) are a high-efficiency, low-cost form of solar technology because of the abundance of useful materials and a simple fabrication procedure relative to other photovoltaic devices. Furthermore, the perovskite material shows decent electron and hole mobilities, a wide absorption range, and long exciton diffusion length. So far, many groups have focused on the research of perovskite thin-film solar cells, and these perovskite solar cells have been deemed to be one of the leading next generation photovoltaic technologies. However, there are several problems that restrict the enhancement of perovskite solar cell performance such as their poor uniformity and low crystallinity. Herein we summarize and discuss the role of film quality on power conversion efficiency, and effect of fabrication condition on the light absorbance of perovskite film.

Di-isopropyl ether assisted crystallization of organic-inorganic perovskites for efficient and reproducible perovskite solar cells

Organic-inorganic perovskite solar cells have emerged as a promising photovoltaic technology because of their advantages such as low cost, high efficiency, and solution processability. The performance of perovskite solar cells is highly dependent on the crystallinity and morphology of the perovskite films. Herein, we report a simple, one-step anti-solvent deposition process using di-isopropyl ether as a dripping solvent to obtain extremely uniform and highly crystalline CH₃NH₃PbI₃ perovskite films. Compared to toluene, chlorobenzene, chloroform, or diethyl ether, di-isopropyl ether has proven to be a more suitable solvent for an anti-solvent deposition process. The perovskite solar cells fabricated by the anti-solvent deposition process using di-isopropyl ether treatment exhibit an average power conversion efficiency (PCE) of 17.67 ± 0.54% and the highest PCE of 19.07%. Moreover, the higher boiling point of di-isopropyl ether makes the anti-solvent deposition process more tolerant to elevated ambient temperature, which can be carried out at ambient temperatures up to 40 °C. Our results demonstrate that di-isopropyl ether is an excellent dripping solvent in the anti-solvent deposition process for efficient and reproducible perovskite solar cells.

One-Step Printable Perovskite Films Fabricated under Ambient Conditions for Efficient and Reproducible Solar Cells

Despite the potential of roll-to-roll processing for the fabrication of perovskite films, the realization of highly efficient and reproducible perovskite solar cells (PeSCs) through continuous coating techniques and low-temperature processing is still challenging. Here, we demonstrate that efficient and reliable CH₃NH₃PbI₃ (MAPbI₃) films fabricated by a printing process can be achieved through synergetic effects of binary processing additives, N-cyclohexyl-2-pyrrolidone (CHP) and dimethyl sulfoxide (DMSO). Notably, these perovskite films are deposited from premixed perovskite solutions for facile one-step processing under a room-temperature and ambient atmosphere. The CHP molecules result in the uniform and homogeneous perovskite films even in the one-step slot-die system, which originate from the high boiling point and low vapor pressure of CHP. Meanwhile, the DMSO molecules facilitate the growth of perovskite grains by forming intermediate states with the perovskite precursor molecules. Consequently, fully printed PeSC based on the binary additive system exhibits a high PCE of 12.56% with a high reproducibility.

Cross-Linkable, Solvent-Resistant Fullerene Contacts for Robust and Efficient Perovskite Solar Cells with Increased JSC and VOC

The active layers of perovskite solar cells are also structural layers and are central to ensuring that the structural integrity of the device is maintained over its operational lifetime. Our work evaluating the fracture energies of conventional and inverted solution-processed MAPbI₃ perovskite solar cells has revealed that the MAPbI₃ perovskite exhibits a fracture resistance of only ∼0.5 J/m², while solar cells containing fullerene electron transport layers fracture at even lower values, below ∼0.25 J/m². To address this weakness, a novel styrene-functionalized fullerene derivative, MPMIC₆₀, has been developed as a replacement for the fragile PC₆₁BM and C₆₀ transport layers. MPMIC₆₀ can be transformed into a solvent-resistant material through curing at 250 °C. As-deposited films of MPMIC₆₀ exhibit a marked 10-fold enhancement in fracture resistance over PC₆₁BM and a 14-fold enhancement over C₆₀. Conventional-geometry perovskite solar cells utilizing cured films of MPMIC₆₀ showed a significant, 205% improvement in fracture resistance while exhibiting only a 7% drop in PCE (13.8% vs 14.8% PCE) in comparison to the C₆₀ control, enabling larger V_OC and J_SC values. Inverted cells fabricated with MPMIC₆₀ exhibited a 438% improvement in fracture resistance with only a 6% reduction in PCE (12.3% vs 13.1%) in comparison to those utilizing PC₆₁BM, again producing a higher J_SC.

Enhanced conversion efficiency in perovskite solar cells by effectively utilizing near infrared light

Up-conversion β-NaYF4:Yb(3+),Tm(3+)/NaYF4 core-shell nanoparticles (NYF NPs) with a high luminous intensity in the visible light region were synthesized by a hydrothermal reaction process. Photocurrent densities of the mesoscopic perovskite solar cells fabricated by incorporating up-conversion NYF NPs into the electron transporting layer are effectively enhanced. The effects of the thicknesses of the electron transporting layer and the weight ratio of up-conversion NYF NPs/TiO2 on the power conversion efficiency (PCE) of the as-fabricated devices were also investigated. The results indicate that the PCE of the optimized device achieves 16.9%, which is 20% higher than that of the device without introducing NYF NPs, and the steady-state PCE of the as-fabricated devices is close to its transient-state PCE. The up-conversion effect of NYF NPs is conducive to higher device performance rather than the nanoparticles as scattering centers to increase possible light absorption of the perovskite film or the electronic effect of the NaYF4 shell surface. These results can be further confirmed by finite-difference time-domain simulation. Photoluminescence results suggest that the multiphonon-assistance can accelerate the nonradiative recombination process at a lower temperature. Incorporating NYF NPs into the electron transporting layer opens a new approach to a promising family of electron transporting materials for mesoscopic perovskite solar cells.

Highly Efficient Flexible Perovskite Solar Cells Using Solution-Derived NiOx Hole Contacts

A solution-derived NiOx film was employed as the hole contact of a flexible organic-inorganic hybrid perovskite solar cell. The NiOx film, which was spin coated from presynthesized NiOx nanoparticles solution, can extract holes and block electrons efficiently, without any other post-treatments. An optimal power conversion efficiency (PCE) of 16.47% was demonstrated in the NiOx-based perovskite solar cell on an ITO-glass substrate, which is much higher than that of the perovskite solar cells using high temperature-derived NiOx film contacts. The low-temperature deposition process made the NiOx films suitable for flexible devices. NiOx-based flexible perovskite solar cells were fabricated on ITO-PEN substrates, and a preliminary PCE of 13.43% was achieved.

TiO2 passivation for improved efficiency and stability of ZnO nanorods based perovskite solar cells

We adopted a wet-chemical method to deposit a TiO₂ passivation layer on ZnO nanorods, and demonstrated drastically improved photovoltaic performance and device stability of ZnO nanorods based perovskite solar cells.

Evolution in surface coverage of CH3NH3PbI3−XClXvia heat assisted solvent vapour treatment and their effects on photovoltaic performance of devices

We demonstrate a facile and well controlled heat assisted solvent vapour treatment (HASVT) method for the growth of compact perovskite layers with good surface coverage areas in ambient atmosphere.