Each component layer in a perovskite solar cell plays an important role in the cell performance. Here, a few types of polymers including representative p‐type and n‐type semiconductors, and a classical insulator, are chosen to dope into a perovskite film. The long‐chain polymer helps to form a network among the perovskite crystalline grains, as witnessed by the improved film morphology and device stability. The dewetting process is greatly suppressed by the cross‐linking effect of the polymer chains, thereby resulting in uniform perovskite films with large grain sizes. Moreover, it is found that the polymer‐doped perovskite shows a reduced trap‐state density, likely due to the polymer effectively passivating the perovskite grain surface. Meanwhile the doped polymer formed a bridge between grains for efficient charge transport. Using this approach, the solar cell efficiency is improved from 17.43% to as high as 19.19%, with a much improved stability. As it is not required for the polymer to have a strict energy level matching with the perovskite, in principle, one may use a variety of polymers for this type of device design.
Parasitic absorption by window layer, electrode layer, and interface layer in the near ultraviolet (UV) region is no longer negligible for high-efficiency perovskite solar cells. On the other hand, UV-induced degradation is also a big component of cell instability. Herein, CsPbCl 3 :Mn-based quantum dots (QDs) are synthesized and applied onto the front side of the perovskite solar cells as the energy-down-shift (EDS) layer. It is found that with very high quantum yield (∼60%) and larger Stokes shift (>200 nm), the CsPbCl 3 :Mn QDs effectively convert the normally wasted energy in the UV region (300−400 nm) into usable visible light at ∼590 nm for enhanced power conversion efficiency (PCE). Meanwhile, conversion of the UV rays eliminated a significant loss mechanism that deteriorates perovskite stability. As a result, external quantum efficiency in the UV region is significantly increased, leading to an increased short-circuit current (3.77%) and PCE (3.34%). Furthermore, the stability of perovskite solar cells has also been improved from 85% to 97% of their initial efficiency after exposure in the UV region with 5 mW/cm 2 intensity by 100 h. In parallel, the organic and silicon solar cells coated by EDS QDs also both confirm the above conclusion with PCE enhancements of 3.21% and 2.98%, respectively. These results suggest that the CsPbCl 3 :Mn QDs play a significant role in improving the efficiency and stability of photovoltaic devices. To our knowledge, this is the first report about CsPbCl 3 :Mn QD-assisted perovskite solar cells.
All-inorganic CsPbBr perovskite solar cells display outstanding stability toward moisture, light soaking, and thermal stressing, demonstrating great potential in tandem solar cells and toward commercialization. Unfortunately, it is still challenging to prepare high-performance CsPbBr films at moderate temperatures. Herein, a uniform, compact CsPbBr film was fabricated using its quantum dot (QD)-based ink precursor. The film was then treated using thiocyanate ethyl acetate (EA) solution in all-ambient conditions to produce a superior CsPbBr-CsPbBr composite film with a larger grain size and minimal defects. The achievement was attributed to the surface dissolution and recrystallization of the existing SCN and EA. More specifically, the SCN ions were first absorbed on the Pb atoms, leading to the dissolution and stripping of Cs and Br ions from the CsPbBr QDs. On the other hand, the EA solution enhances the diffusion dynamics of surface atoms and the surfactant species. It is found that a small amount of CsPbBr in the composite film gives the best surface passivation, while the Br-rich surface decreases Br vacancies (V) for a prolonged carrier lifetime. As a result, the fabricated device gives a higher solar cell efficiency of 6.81% with an outstanding long-term stability.
Comparing to other carbon materials, the general graphyne structure is much superior in terms of adaptable bandgap, uniformly distributed pores, more design flexibility, easier for chemical synthesis, pliable electronic properties, and smaller atomic density. Herein, novel γ‐graphdiyne quantum dots (GD QDs) are used in perovskite solar cells as a surface modifier or dopant to TiO2, CH3NH3PbI3, and Spiro‐OMeTAD to realize multiple advantageous effects, in hoping that it would form a more effective carrier transport channel for boosted solar cell performance. First, the presence of GD QDs on TiO2 surface increases perovskite grain size for higher current density and fill factor. Second, the GD QDs at each interface reduce the conduction band offset, passivate the surface for suppressed carrier recombination to attain higher open‐circuit voltage. Third, it improves hydrophobicity and eliminates pinholes in the Spiro‐OMeTAD film for enhanced solar cell stability. As a result, the optimized device shows >15% enhancement in power conversion efficiency (from 17.17 to 19.89%) comparing to the reference device. More significantly, the device stability was improved in harsh environment (moist air, UV irradiation, or thermal conditions). It is expected that GD QDs will find their applications in efficient and stable perovskite solar cells and optoelectronic devices.
Photodetectors (PDs), especially those that respond in the infrared region, are highly desirable and have a wide range of applications ranging from cell phones, cameras, and home electronics to airplanes and satellites. Herein, we designed and fabricated PDs based on air-stable α-CsPbI QDs and an up-conversion material (NaYF:Yb,Er QDs) using a facial low temperature spin-coating method. When the α-CsPbI QDs are surface-modified using NaYF:Yb,Er QDs, their optical response is extended to the NIR region to allow broadband application from the UV to visible to NIR region (260 nm-1100 nm). The optoelectronic properties and compositional stability of the devices were also studied in detail. From the results, the PDs are capable of broad-bandwidth photodetection from the deep UV to NIR region (260 nm-1100 nm) with good photoresponsivity (R, 1.5 A W), high on/off ratio (up to 10) and very short rise/decay time (less than 5 ms/5 ms). It was found that the photoresponsivity performance of the PDs in this work is better than that of all the other previously reported perovskite QD-based PDs with a lateral device structure. Furthermore, the device performance shows very little degradation over the course of 60 days of storage under ambient conditions. The combination of remarkable stability, high performance broad-bandwidth photodetection, and easy fabrication suggest that these QDs are a very promising semiconducting candidate for optoelectronic applications.
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