Cesium Acetate-Induced Interfacial Compositional Change and Graded Band Level in MAPbI3 Perovskite Solar Cells

Compositional engineering and interfacial modifications have played pivotal roles in the accomplishment of high-efficiency perovskite solar cells (PSCs). Different interfaces in the PSCs influence the performance remarkably either by altering the crystallization of the active material or shifting the energy levels or improving the electrical contact. This work reports how a thin layer of cesium acetate on the TiO₂ electron transport layer (ETL) induces generation of a PbI₂-rich methylammonium lead iodide (MAPbI₃) composition at the ETL/MAPbI₃ interface, which downshifts the conduction band level of MAPbI₃ to create an energy level gradient favorable for carrier collection, resulting in higher photocurrent, fill factor, and overall power conversion efficiency.

Enhancing Thermal Oxidation Stability of Silver Nanowire Transparent Electrodes by Using a Cesium Carbonate-Incorporated Overcoating Layer

Despite their excellent electrical and optical properties, Ag nanowires (NWs) suffer from oxidation when exposed to air for several days. In this study, we synthesized a Cs carbonate-incorporated overcoating layer by spin-coating and ultraviolet curing to prevent the thermal oxidation of Ag NWs. Cs incorporation increased the decomposition temperature of the overcoating layer, thus enhancing its thermal resistance. The effects of the Cs carbonate-incorporated overcoating layer on the optoelectrical properties and stability of Ag NWs were investigated in detail. The Ag NW electrode reinforced with the Cs carbonate-incorporated overcoating layer exhibited excellent thermal oxidation stability after exposure to air for 55 days at 85 °C and a relative humidity of 85%. The novel overcoating layer synthesized in this study is a promising passivation layer for Ag NWs against thermal oxidation under ambient conditions. This overcoating layer can be applied in large-area optoelectronic devices based on Ag NW electrodes.

Efficient TiO2 Surface Treatment Using Cs2CO3 for Solution-Processed Planar-Type Sb2S3 Solar Cells

We report a highly effective surface treatment method for planar-type Sb₂S₃ solar cells by employing a Cs₂CO₃-modified compact TiO₂ (c-TiO₂) electron transport layer. It is found that surface treatment using a Cs₂CO₃ solution can shift the work function of c-TiO₂ upward and reduce its surface roughness. As a result, compared with the power conversion efficiency of untreated solar cells, that of the treated solar cells with a glass/FTO/c-TiO₂(/Cs₂CO₃)/Sb₂S₃/P3HT/Au structure significantly improved from 2.83 to 3.97%. This study demonstrates that the introduction of Cs₂CO₃ on a c-TiO₂ layer is a simple and efficient way to adjust the work function of the electron transport layer and fabricate high-performance planar-type Sb₂S₃ solar cells.

Enhanced Performance of Perovskite Solar Cells by Using Ultrathin BaTiO3 Interface Modification

Efficiency promotion has been severely constrained by charge recombination in perovskite solar cells (PSCs). Interface modification has been proved to be an effective way to reduce the interfacial charge recombination. In this work, a mesoporous TiO₂ (mp-TiO₂) layer was modified by an ultrathin BaTiO₃ layer to suppress charge recombination in PSCs. The ultrathin BaTiO₃ modification layer was prepared by the spin coating method using a barium salt solution. The concentration of the barium salt solution was optimized, and the effect of the BaTiO₃ modification layer on the performance of the cells was also investigated. The modification layer can not only successfully retard charge recombination but also effectively boost the rate of electron extraction at the interface, resulting in enhanced open-circuit voltage ( V_oc), short circuit current density ( J_sc), and fill factor. Furthermore, the hysteresis of the PSCs was also significantly reduced after the modification. By optimizing and employing the BaTiO₃ modification layer, the power conversion efficiency of the cells was increased from 16.13 to 17.87%.

Recent Advance in Solution-Processed Organic Interlayers for High-Performance Planar Perovskite Solar Cells

Planar heterojunction perovskite solar cells (PSCs) provide great potential for fabricating high-efficiency, low-cost, large-area, and flexible photovoltaic devices. In planar PSCs, a perovskite absorber is sandwiched between hole and electron transport materials. The charge-transporting interlayers play an important role in enhancing charge extraction, transport, and collection. Organic interlayers including small molecules and polymers offer great advantages for their tunable chemical/electronic structures and low-temperature solution processibility. Here, recent progress of organic interlayers in planar heterojunction PSCs is discussed, and the effect of chemical structures on device performance is also illuminated. Finally, the main challenges in developing planar heterojunction PSCs based on organic interlayers are identified, and strategies for enhancing the device performance are also proposed.

Enhanced Charge Carrier Transport and Device Performance Through Dual-Cesium Doping in Mixed-Cation Perovskite Solar Cells with Near Unity Free Carrier Ratios

PbI₂-enriched mixed perovskite film [FA_0.81MA_0.15Pb(I_0.836Br_0.15)₃] has been widely studied due to its great potential in perovskite solar cell (PSC) applications. Herein, a FA_0.81MA_0.15Pb(I_0.836Br_0.15)₃ film has been fabricated with the temperature-dependent optical absorption spectra utilized to determine its exciton binding energy. A ∼13 meV exciton binding energy is estimated, and a near-unity fraction of free carriers out of the total photoexcitons has been obtained in the solar cell operating regime at equilibrium state. PSCs are fabricated with this mixed perovskite film, but a significant electron transport barrier at the TiO₂-perovskite interface limited their performance. Cs₂CO₃ and CsI are then utilized as functional enhancers with which to substantially balance the electron and hole transport and increase the carriers (both electrons and holes) mobilities in PSCs, resulting in much-improved solar-cell performance. The modified PSCs exhibit reproducible power conversion efficiency (PCE) values with little hysteresis effect in the J-V curves, achieving PCEs up to 19.5% for the Cs₂CO₃-modified PSC and 20.6% when subsequently further doped with CsI.

WO3 Nanoparticles or Nanorods Incorporating Cs2CO3/PCBM Buffer Bilayer as Carriers Transporting Materials for Perovskite Solar Cells

In this work, we demonstrate a novel carrier transporting combination made of tungsten trioxide (WO₃) nanomaterials and Cs₂CO₃/PCBM buffer bilayer for the fabrication of perovskite solar cells (PSCs). Two different types of WO₃, including nanoparticles and nanorods, were prepared by sol-gel process and hydrothermal method, respectively. Cs₂CO₃/PCBM buffer bilayer was inserted between WO₃ and perovskite layers to improve charge transfer efficiency and formation of pinhole-free perovskite layer. Besides, the leakage current of the devices containing Cs₂CO₃/PCBM buffer bilayer was significantly suppressed. The optimized device based on WO₃ nanoparticles and Cs₂CO₃/PCBM bilayer showed an open-circuit voltage of 0.84 V, a short-circuit current density of 20.40 mA/cm², a fill factor of 0.61, and a power conversion efficiency of 10.49 %, which were significantly higher than those of PSCs without Cs₂CO₃/PCBM buffer bilayer. The results revealed that the combination of WO₃ nanomaterials and Cs₂CO₃/PCBM bilayer provides an effective solution for improving performances of PSCs.

Thermally Stable Mesoporous Perovskite Solar Cells Incorporating Low-Temperature Processed Graphene/Polymer Electron Transporting Layer

In the short time since its discovery, perovskite solar cells (PSCs) have attained high power conversion efficiency but their lack of thermal stability remains a barrier to commercialization. Among the experimentally accessible parameter spaces for optimizing performance, identifying an electron transport layer (ETL) that forms a thermally stable interface with perovskite and which is solution-processable at low-temperature will certainly be advantageous. Herein, we developed a mesoporous graphene/polymer composite with these advantages when used as ETL in CH₃NH₃PbI₃ PSCs, and a high efficiency of 13.8% under AM 1.5G solar illumination could be obtained. Due to the high heat transmission coefficient and low isoelectric point of mesoporous graphene-based ETL, the PSC device enjoys good chemical and thermal stability. Our work demonstrates that the mesoporous graphene-based scaffold is a promising ETL candidate for high performance and thermally stable PSCs.

Organic-inorganic hybrid lead halide perovskites for optoelectronic and electronic applications

Organic and inorganic hybrid perovskites (e.g., CH(3)NH(3)PbI(3)), with advantages of facile processing, tunable bandgaps, and superior charge-transfer properties, have emerged as a new class of revolutionary optoelectronic semiconductors promising for various applications. Perovskite solar cells constructed with a variety of configurations have demonstrated unprecedented progress in efficiency, reaching about 20% from multiple groups after only several years of active research. A key to this success is the development of various solution-synthesis and film-deposition techniques for controlling the morphology and composition of hybrid perovskites. The rapid progress in material synthesis and device fabrication has also promoted the development of other optoelectronic applications including light-emitting diodes, photodetectors, and transistors. Both experimental and theoretical investigations on organic-inorganic hybrid perovskites have enabled some critical fundamental understandings of this material system. Recent studies have also demonstrated progress in addressing the potential stability issue, which has been identified as a main challenge for future research on halide perovskites. Here, we review recent progress on hybrid perovskites including basic chemical and crystal structures, chemical synthesis of bulk/nanocrystals and thin films with their chemical and physical properties, device configurations, operation principles for various optoelectronic applications (with a focus on solar cells), and photophysics of charge-carrier dynamics. We also discuss the importance of further understanding of the fundamental properties of hybrid perovskites, especially those related to chemical and structural stabilities.

Solution-processed carrier selective layers for high efficiency organic/nanostructured-silicon hybrid solar cells

The reduction of interface minority carrier recombination is regarded as a key performance indicator in improving the power conversion efficiency (PCE) of organic-inorganic hybrid solar cells. In this study, we chose two kinds of carrier-selective layers to be applied in a hybrid solar cell device. A hole selective transporting layer of N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) was added to the interface between Si nanohole structures and

PEDOT

PSS, and the electron selective layer cesium carbonate (Cs2CO3) was added to the interface between the backside Si wafer and the rear Ti/Ag electrode. The main process used a clean and low-cost solution process, and the annealed temperature was under 140 °C. In addition, after we inserted these two carrier selective layers, the minority carrier lifetime was prolonged from 29.98 μs to 140.81 μs, indicating its significance in reducing the recombination rate. Eventually, we demonstrated that the PCE of Si/organic heterojunction solar cells can be improved to 13.23%.

Efficient perovskite solar cells via simple interfacial modification toward a mesoporous TiO2 electron transportation layer

Enhanced performance of a perovskite solar cell via simple interfacial modification onto a mesoporous TiO₂ layer.

Highly reproducible perovskite solar cells with excellent CH3NH3PbI3−xClx film morphology fabricated via high precursor concentration

A novel method was proposed to achieve excellent CH₃NH₃PbI_3−xClx films based on a high concentration spinning process, which offered an effective strategy for highly reproducible perovskite solar cells with excellent morphology.