An ITO-Free Kesterite Solar Cell.

Photovoltaic thin film solar cells based on kesterite Cu2 ZnSn(S, Se)4 (CZTSSe) have reached 13.8% sunlight-to-electricity conversion efficiency. However, this efficiency is still far from the Shockley-Queisser radiative limit and is hindered by the significant deficit in open circuit voltage (VOC ). The presence of high-density interface states between the absorber layer and buffer or window layer leads to the recombination of photogenerated carriers, thereby reducing effective carrier collection. To tackle this issue, a new window structure ZnO/AgNW/ZnO/AgNW (ZAZA) comprising layers of ZnO and silver nanowires (AgNWs) is proposed. This structure offers a simple and low-damage processing method, resulting in improved optoelectronic properties and junction quality. The ZAZA-based devices exhibit enhanced VOC due to the higher built-in voltage (Vbi ) and reduced interface recombination compared to the usual indium tin oxide (ITO) based structures. Additionally, improved carrier collection is demonstrated as a result of the shortened collection paths and the more uniform carrier lifetime distribution. These advances enable the fabrication of the first ITO-free CZTSSe solar cells with over 10% efficiency without an anti-reflective coating.

Ratio-Tuning of Silica Aerogel Co-Hydrolyzed Precursors Enables Broadband, Angle-Independent, Deformation-Tolerant, Achieving 99.7% Reflectivity.

The super-white body might be defined as its reflectivity exceeding 98% at any angle in the visible light spectrum, which can be used in a variety of emerging fields including optics, energy, environment, aerospace, etc. However, elaborate synthesis of a light-weight, highly reflective super-white aerogel body remains a great challenge. In this work, fine-tuning of silica aerogel co-hydrolyzed precursor ratios, 99.7% reflectivity with angle-independence in the visible light spectrum has been successfully achieved when the areal density is only 0.129 g cm-2 , which breaks through the theoretical bandwidth limit of photonic crystals as well as the measured reflectivity limit of conventional porous materials. Furthermore, the reflectivity of super-white silica aerogel remains unchanged after various harsh deformations including compression and bending 1000 times, solar (≈800 W m-2 ), ultraviolet (≈0.68 W m-2 ), and humidity (100%) aging for 100 days, liquid nitrogen (-196 °C) and high-temperature (300 °C) thermal shock 100 times. As proofs of performance, the resulting super-white silica aerogels have been used as the novel standard white plate  for better spectrum calibration, as the flexible projector curtains for optical display, as well as the transmitted light reflective layer in the photovoltaic cell for improving the relative power conversion efficiency of 5.6%.

Solution Processed Semi-Transparent Organic Solar Cells Over 50% Visible Transmittance Enabled by Silver Nanowire Electrode with Sandwich Structure.

Photovoltaic windows with easy installation for the power supply of household appliances have long been a desire of energy researchers. However, due to the lack of top electrodes that offer both high transparency and low sheet resistance, the development of high-transparency photovoltaic windows for indoor lighting scenarios has lagged significantly behind photovoltaic windows where privacy issues are involved. Addressing this issue, this work develops a solution-processable transparent top electrode using sandwich structure silver nanowires, realizing high transparency in semi-transparent organic solar cells. The wettability and conducting properties of the electrode are improved by a modified hole-transport layer named HP. The semi-transparent solar cell exhibits good see-through properties at a high average visible transmittance of 50.8%, with power conversion efficiency of 7.34%, and light utilization efficiency of 3.73%, which is the highest without optical modulations. Moreover, flexible devices based on the above-mentioned architecture also show excellent mechanical tolerance compared with Ag electrode counterparts, which retains 94.5% of their original efficiency after 1500 bending cycles. This work provides a valuable approach for fabricating solution-processed high transparency organic solar cells, which is essential in future applications in building integrated photovoltaics.

In situ performance and stability tests of large-area flexible polymer solar cells in the 35-km stratospheric environment.

Flexible organic solar cells (FOSCs) are one of the most promising power sources for aerospace aircraft due to their attractive advantages with high power-per-weight ratio and excellent mechanical flexibility. Understanding the performance and stability of high-performance FOSCs is essential for the further development of FOSCs for aerospace applications. In this paper, after systematic investigations on the performance of the state-of-the-art high-performance solar cells under thermal cycle and intensive UV irradiation conditions, in situ performance and stability tests of the solar cells in the 35 km stratospheric environment were carried out through a high-altitude balloon uploading. The encapsulated FOSCs with an area of 0.64 cm2 gave the highest power density of 15.26 mW/cm2 and an efficiency over 11%, corresponding to a power-per-weight ratio of over 3.32 kW/kg. More importantly, the cells showed stable power output during the 3-h continuous flight at 35 km and only 10% performance decay after return to the lab, suggesting promising stability of the FOSCs in the stratospheric environment.

12.42% Monolithic 25.42 cm2 Flexible Organic Solar Cells Enabled by an Amorphous ITO-Modified Metal Grid Electrode.

Printed metal nanogrid electrode exhibits superior characteristics for use in flexible organic solar cells (OSCs). However, the high surface roughness and inhomogeneity between grid and blank region is adverse for performance improvement. In this work, a thin amorphous indium tin oxide (ITO) film (α-ITO) is introduced to fill the blank and to improve the charge transporting. The introduction of α-ITO significantly improves the comprehensive properties of metal grid electrode, which exhibits excellent bending resistance and long-term stability under double 85 condition (under 85 °C and 85% relative humidity) for 200 h. Both experimental and simulation results reveal α-ITO with a sheet resistance of 20 000 Ω â–¡-1 is sufficient to improve the charge transporting within the adjacent grids, leading to a remarkable efficiency of 16.54% for 1 cm2 flexible devices. With area increased to 4.00, 9.00, and 25.42 cm2 , the devices still display a performance of 16.22%, 14.69%, and 12.42%, respectively, showing less efficiency loss during upscaling. And the 25.42 cm2 monolithic flexible device exhibits a certificated efficiency of 12.03%. Moreover, the device shows significantly improved air stability relative to conventional high-conductive poly(3,4-ethylenedioxythiophene):polystyrene sulfonate-modified device. All these make the α-ITO-modified Ag/Cu electrode promise to achieve high-efficient and long-term stable large-area flexible OSCs.

Efficiency above 12% for 1 cm2 Flexible Organic Solar Cells with Ag/Cu Grid Transparent Conducting Electrode.

With the rapid progress of organic solar cells (OSCs), improvement in the efficiency of large-area flexible OSCs (>1 cm2) is crucial for real applications. However, the development of the large-area flexible OSCs severely lags behind the growth of the small-area OSCs, with the electrical loss due to the large sheet resistance of the electrode being a main reason. Herein, a high conductive and high transparent Ag/Cu composite grid with sheet resistance <1 Ω sq-1 and an average visible light transparency of 84% is produced as the transparent conducting electrode of flexible OSCs. Based on this Ag/Cu composite grid electrode, a high efficiency of 12.26% for 1 cm2 flexible OSCs is achieved. The performances of large-area flexible OSCs also reach 7.79% (4 cm2) and 7.35% (9 cm2), respectively, which are much higher than those of the control devices with conventional flexible indium tin oxide electrodes. Surface planarization using highly conductive PEDOT:PSS and modification of the ZnO buffer layer by zirconium acetylacetonate (ZrAcac) are two necessary steps to achieve high performance. The flexible OSCs employing Ag/Cu grid have excellent mechanical bending resistance, maintaining high performance after bending at a radius of 2 mm.