Coevaporation of doped inorganic carrier-selective layers for high-performance inverted planar perovskite solar cells

Inorganic carrier selective layers (CSLs), whose conductivity can be effectively tuned by doping, offer low-cost and stable alternatives for their organic counterparts in perovskite solar cells (PSCs). Herein, we employ a dual-source electron-beam co-evaporation method for the controlled deposition of copper-doped nickel oxide (Cu:NiO) and tungsten-doped niobium oxide (W:Nb2O5) as hole and electron transport layers, respectively. The mechanisms for the improved conductivity using dopants are investigated. Owing to the improved conductivity and optimized band alignment of the doped CSLs, the all-inorganic-CSLs-based PSCs achieves a maximum power conversion efficiency (PCE) of 20.47%. Furthermore, a thin titanium buffer layer is inserted between the W:Nb2O5 and the silver electrode to prevent the halide ingression and improve band alignment. This leads to a further improvement of PCE to 21.32% and a long-term stability (1200 h) after encapsulation. Finally, the large-scale applicability of the doped CSLs by co-evaporation is demonstrated for the device with 1 cm2 area showing a PCE of over 19%. Our results demonstrate the potential application of the co-evaporated CSLs with controlled doping in PSCs for commercialization

High-performance transparent ultraviolet photodetectors based on inorganic perovskite CsPbCl3 nanocrystals

Inorganic lead halide perovskite nanocrystals (CsPbCl3 NCs) with excellent ultraviolet (UV) light absorption, high carrier mobility, long carrier diffusion lengths, and long-term stability are good candidates as smart materials for transparent optoelectronic devices. In this study, transparent UV photodetectors (PDs) based on CsPbCl3 NCs were fabricated for the first time. The optimized device exhibited visible light transmittance approximately 90%, strong absorption of UV light in the wavelength from 300 nm to 410 nm, good photoresponsivity (1.89 A W-1), and a high on/off ratio (up to 103). Meanwhile, the rise and decay response times of the device were less than 41 ms and 43 ms, respectively. Furthermore, we performed detailed analysis of the effects by employing CsPbCl3 NCs in assembled films and final devices using various characterization methods. The simple fabrication and remarkable UV photodetection capabilities of CsPbCl3 NCs make them promising semiconducting candidates in optoelectronic applications

Spatiotemporal Evolution of Carbon Emissions According to Major Function-Oriented Zones: A Case Study of Guangdong Province, China

Studying the spatiotemporal evolution of carbon emissions from the perspective of major function-oriented zones (MFOZs) is crucial for making a carbon reduction policy. However, most previous research has ignored the spatial characteristics and MFOZ influence. Using statistical and spatial analysis tools, we explored the spatiotemporal characteristics of carbon emissions in Guangdong Province from 2001 to 2021. The following results were obtained: (1) Carbon emissions fluctuated from 2020 to 2021 because of COVID-19. (2) Over the last 20 years, the proportion of carbon emissions from urbanization development zones (UDZs) has gradually decreased, whereas those of the main agricultural production zones (MAPZs) and key ecological function zones (KEFZs) have increased. (3) Carbon emissions efficiency differed significantly among the three MFOZs. (4) Carbon emissions from coastal UDZs were increasingly apparent; however, the directional characteristics of MAPZ and KEFZ emissions were not remarkable. (5) Carbon transfer existed among the three kinds of MFOZs, resulting in the economy and carbon emissions being considerably misaligned across Guangdong Province. These results indicated that the MFOZ is noteworthy in revealing how carbon emissions evolved. Furthermore, spatiotemporal characteristics, especially spatial characteristics, can help formulate carbon reduction policies for realizing carbon peak and neutrality goals in Guangdong Province

ITIC surface modification to achieve synergistic electron transport layer enhancement for planar-type perovskite solar cells with efficiency exceeding 20%

The electron transport layer (ETL), which also serves as the hole-blocking layer, is a key component in planar perovskite solar cells (PSCs). The commonly used ETL is an anatase-TiO2 (an-TiO2) film due to its excellent optical transmittance, chemical stability and semi-conducting characteristics. Nevertheless, its rough surface and plenty of surface defects often lead to a substandard perovskite film and large J-V hysteresis. Herein, a novel low-trap-density ETL is developed by surface modification of the an-TiO2 film using small-molecular ITIC. As a result, the device efficiency has been dramatically increased from 17.12% to 20.08%, entering the league of the highest planar-type perovskite cells. Moreover, the J-V hysteresis has been significantly reduced. Further investigation shows that the ITIC smoothens the TiO2 surface, passivates defects or dangling bands parasitizing the TiO2 surface, and optimizes the device band alignment. In addition, it is demonstrated that the thin ITIC promotes the formation of high quality, uniform perovskite films with better surface coverage and large grain size, implying that there is a synergistic effect between the low-trap-density ITIC and high-mobility TiO2 in improved PSC performance

ITIC surface modification to achieve synergistic electron transport layer enhancement for planar-type perovskite solar cells with efficiency exceeding 20%

The electron transport layer (ETL), which also serves as the hole-blocking layer, is a key component in planar perovskite solar cells (PSCs). The commonly used ETL is an anatase-TiO2 (an-TiO2) film due to its excellent optical transmittance, chemical stability and semi-conducting characteristics. Nevertheless, its rough surface and plenty of surface defects often lead to a substandard perovskite film and large J-V hysteresis. Herein, a novel low-trap-density ETL is developed by surface modification of the an-TiO2 film using small-molecular ITIC. As a result, the device efficiency has been dramatically increased from 17.12% to 20.08%, entering the league of the highest planar-type perovskite cells. Moreover, the J-V hysteresis has been significantly reduced. Further investigation shows that the ITIC smoothens the TiO2 surface, passivates defects or dangling bands parasitizing the TiO2 surface, and optimizes the device band alignment. In addition, it is demonstrated that the thin ITIC promotes the formation of high quality, uniform perovskite films with better surface coverage and large grain size, implying that there is a synergistic effect between the low-trap-density ITIC and high-mobility TiO2 in improved PSC performance

Polymer Doping for High-Efficiency Perovskite Solar Cells with Improved Moisture Stability

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

Magnetic Field-Assisted Perovskite Film Preparation for Enhanced Performance of Solar Cells

Perovskite solar cells (PSCs) are promising low-cost photovoltaic technologies with high power conversion efficiency (PCE). The crystalline quality of perovskite materials is crucial to the photovoltaic performance of the PSCs. Herein, a simple approach is introduced to prepare high-quality CH₃NH₃PbI₃ perovskite films with larger crystalline grains and longer carriers lifetime by using magnetic field to control the nucleation and crystal growth. The fabricated planar CH₃NH₃PbI₃ solar cells have an average PCE of 17.84% and the highest PCE of 18.56% using an optimized magnetic field at 80 mT. In contrast, the PSCs fabricated without the magnetic field give an average PCE of 15.52% and the highest PCE of 16.72%. The magnetic field action produces an ordered arrangement of the perovskite ions, improving the crystallinity of the perovskite films and resulting in a higher PCE