Graded Heterojunction Improves Wide-Bandgap Perovskite for Highly Efficient 4-Terminal Perovskite/Silicon Tandem Solar Cells.

Wide-bandgap (WBG) perovskite solar cells (PSCs) are essential for highly efficient and stable silicon/perovskite tandem solar cells. In this study, we adopted a synthetic strategy with lead thiocyanate (Pb(SCN)2) additive and methylammonium chloride (MACl) posttreatment to enhance the crystallinity and improve the interface of WBG perovskite films with a bandgap of 1.68 eV. The excessive PbI2 was formed at grain boundaries and converted into MAPbI3-xClx perovskites, which are utilized to form the graded heterojunction (GHJ) and compressive strain. This is beneficial for passivating nonradiative recombination defects, suppressing halide phase segregation, and facilitating carrier extraction. Subsequently, the device with GHJ delivered a champion efficiency of 20.30% and superior stability in ambient air and under 85 °C. Finally, we achieved a recorded efficiency of 30.91% for 4-terminal WBG perovskite/TOPCon tandem silicon solar cells. Our findings demonstrate a promising approach for fabricating efficient and stable WBG PSCs through the formation of GHJ.

Performance Enhancement of All-Inorganic Carbon-Based CsPbIBr2 Perovskite Solar Cells Using a Moth-Eye Anti-Reflector.

All-inorganic carbon-based CsPbIBr2 perovskite solar cells (PSCs) have attracted increasing interest due to the low cost and the balance between bandgap and stability. However, the relatively narrow light absorption range (300 to 600 nm) limited the further improvement of short-circuit current density (JSC) and power conversion efficiency (PCE) of PSCs. Considering the inevitable reflectance loss (~10%) at air/glass interface, we prepared the moth-eye anti-reflector by ultraviolet nanoimprint technology and achieved an average reflectance as low as 5.15%. By attaching the anti-reflector on the glass side of PSCs, the JSC was promoted by 9.4% from 10.89 mA/cm2 to 11.91 mA/cm2, which is the highest among PSCs with a structure of glass/FTO/c-TiO2/CsPbIBr2/Carbon, and the PCE was enhanced by 9.9% from 9.17% to 10.08%. The results demonstrated that the larger JSC induced by the optical reflectance modulation of moth-eye anti-reflector was responsible for the improved PCE. Simultaneously, this moth-eye anti-reflector can withstand a high temperature up to 200 °C, and perform efficiently at a wide range of incident angles from 40° to 90° and under various light intensities. This work is helpful to further improve the performance of CsPbIBr2 PSCs by optical modulation and boost the possible application of wide-range-wavelength anti-reflector in single and multi-junction solar cells.

Suppressing Halide Phase Segregation in CsPbIBr2 Films by Polymer Modification for Hysteresis-Less All-Inorganic Perovskite Solar Cells.

All-inorganic perovskite CsPbIBr2 materials are promising for optoelectronics, owing to their upgraded ambient stability and suitable bandgap. Unfortunately, they generally undergo severe halide phase segregation under illumination, which creates many iodide-rich and bromide-rich domains coupled with significant deterioration of their optical/electrical properties. Herein, we propose a facile and effective strategy to overcome the halide phase segregation in the CsPbIBr2 film by modifying its crystalline grains with poly(methyl methacrylate) (PMMA) for the first time. Such a strategy is proceeded by covering a PMMA layer on the substrate before deposition of the CsPbIBr2 film. Further investigations manifest that the CsPbIBr2 film with PMMA possesses larger grains, better crystallinity, and fewer traps than the one without any modification. Moreover, it holds the nearly eliminated halide phase segregation. Therefore, the carbon-based, all-inorganic CsPbIBr2 perovskite solar cell exhibits the much suppressed photocurrent hysteresis, coupled with an outstanding efficiency of 9.21% and a high photovoltage of 1.307 V.

Dual-Phase CsPbCl3-Cs4PbCl6 Perovskite Films for Self-Powered, Visible-Blind UV Photodetectors with Fast Response.

All-inorganic, Cl-based perovskites are promising for visible-blind UV photodetectors (PDs), particularly the self-powered ones. However, the devices are rarely reported until now since the low solubility of raw materials hinders significantly the thickness and electronic quality of solution-processed Cl-based perovskite films. Herein, we demonstrate a simple intermediate phase halide exchange method to prepare desired dual-phase CsPbCl3-Cs4PbCl6 films. It is achieved by spin-coating of a certain dose of CH3NH3Cl/CsCl solution onto a CsI-PbBr2-dimethyl sulfoxide (DMSO) intermediate phase film, followed by thermal annealing. The inclusion of CsCl species in the solution is crucial to a stable dual-phase CsPbCl3-Cs4PbCl6 film, while a high annealing temperature contributes to improving its quality. Therefore, the dual-phase CsPbCl3-Cs4PbCl6 film with an absorption onset of ∼420 nm, microsized grains, a few defects, and a proper work function is obtained by optimizing the annealing temperature. The final self-powered, visible-blind UV PD exhibits the superior performance, including a favored response range of 310-420 nm, a high responsivity (R) peak value of 61.8 mA W-1, an exceptional specific detectivity (D*) maximum of 1.35 × 1012 Jones, and a particularly fast response speed of 2.1/5.3 µs, together with amazing operational stability. This work represents the first demonstration of solution-processed, self-powered, visible-blind UV PDs with all-inorganic, Cl-based perovskite films.

Recycling of FTO/TiO2 Substrates: Route toward Simultaneously High-Performance and Cost-Efficient Carbon-Based, All-Inorganic CsPbIBr2 Solar Cells.

Carbon-based, all-inorganic perovskite solar cells (PSCs) have drawn enormous attention recently on account of their ungraded stability and reduced costs. However, their power conversion efficiencies (PCEs) still lag behind the ones with conventional architecture. Moreover, the high cost of FTO substrates and energy-consuming sintering process of TiO2 electron-transporting layers should be further addressed. Herein, it is demonstrated that the FTO/TiO2 substrates could be separated simply from degraded CsPbIBr2 PSCs for fabricating the new ones again, which thus reduces the production costs of resulting PSCs and makes them renewable and sustainable. Meanwhile, the characterization results reveal that there are some residual CsPbIBr2-derived species on recycled FTO/TiO2 substrates, which enable the upper CsPbIBr2 films with suppressed halide phase separation and reduced defects, the diminished work function of TiO2 layers from 4.13 to 3.89 eV, along with decreased conduction band minimum (CBM) difference of CsPbIBr2/TiO2 interface from 0.51 to 0.36 eV. Consequently, the average PCE of CsPbIBr2 PSCs is improved by 20%, from 6.51 ± 0.62% to 8.14 ± 0.63%, wherein the champion one yields the exceptional value of 9.12%. These findings provide an avenue for simultaneous performance enhancement and cost-saving of carbon-based, all-inorganic PSCs to promote their commercialization.

Interfacial Voids Trigger Carbon-Based, All-Inorganic CsPbIBr2 Perovskite Solar Cells with Photovoltage Exceeding 1.33 V.

A novel interface design is proposed for carbon-based, all-inorganic CsPbIBr2 perovskite solar cells (PSCs) by introducing interfacial voids between TiO2 electron transport layer and CsPbIBr2 absorber. Compared with the general interfacial engineering strategies, this design exempts any extra modification layer in final PSC. More importantly, the interfacial voids produced by thermal decomposition of 2-phenylethylammonium iodide trigger three beneficial effects. First, they promote the light scattering in CsPbIBr2 film and thereby boost absorption ability of the resulting CsPbIBr2 PSCs. Second, they suppress recombination of charge carriers and thus reduce dark saturation current density (J0) of the PSCs. Third, interfacial voids enlarge built-in potential (Vbi) of the PSCs, awarding increased driving force for dissociating photo-generated charge carriers. Consequently, the PSC yields the optimized efficiency of 10.20% coupled with an open-circuit voltage (Voc) of 1.338 V. The Voc achieved herein represents the best value among CsPbIBr2 PSCs reported earlier. Meanwhile, the non-encapsulated PSCs exhibit an excellent stability against light, thermal, and humidity stresses, since it remains ~ 97% or ~ 94% of its initial efficiency after being heated at 85 °C for 12 h or stored in ambient atmosphere with relative humidity of 30-40% for 60 days, respectively.

Band Alignment Engineering Towards High Efficiency Carbon-Based Inorganic Planar CsPbIBr2 Perovskite Solar Cells.

Perovskite CsPbIBr2 is attracting ever-increasing attention for carbon-based, all-inorganic solar cells, owing to its well-balanced band gap and stability features. However, significant interfacial recombination of charge carriers in solar cells fabricated with this active layer, which is intrinsically associated with the unwanted conduction band misalignment between CsPbIBr2 and the commonly used TiO2 electron transport layer, has limited power conversion efficiency (PCE) values. Herein, we demonstrate successful conduction band alignment engineering at the TiO2 /CsPbIBr2 heterojunction by modifying TiO2 with CsBr clusters. Such modification triggers a beneficial increase in the conduction band minimum (CBM) of TiO2 from -4.00 to -3.81 eV and decreases the work function from 4.11 to 3.86 eV, thus promoting favorable band alignment at the heterojunction, suppressing recombination, and improving extraction and transport of charge carriers. As a result, the carbon-based, all-inorganic CsPbIBr2 solar cells exhibit over 20 % enhancement in average PCE. The champion device achieves a PCE of 10.71 %, a record among pure CsPbIBr2 -based cells, open-circuit voltage of 1.261 V, and excellent stability.