Strategies for high-performance perovskite solar cells from materials, film engineering to carrier dynamics and photon management

In recent years,halide perovskite solar cells(HPSCs)have attracted a great atten-tion due to their superior photoelectric performance and the low-cost of processing their quality films.In order to commercialize HPSCs,the researchers are focusing on developing high-performance HPSCs.Many strategies have been reported to increase the power conversion efficiency and the long-term stability of HPSCs over the past decade.Herein,we review the latest efforts and the chemical-physical principles for preparing high-efficiency and long-term stability HPSCs in particu-lar,concentrating on the perovskite materials,technologies for perovskite films,charge transport materials and ferroelectric effect to reduce the carrier loss,and photon management via plasmonic and upconversion effects.Finally,the key issues for future researches of HPSCs are also discussed with regard to the require-ments in practical application.

Efficient Monolithic Perovskite/Silicon Tandem Photovoltaics

Tunable bandgaps make halide perovskites promising candidates for developing tandem solar cells(TSCs),a strategy to break the radiative limit of 33.7%for single-junction solar cells.Combining perovskites with market-dominant crystalline silicon(c-Si)is particularly attractive;simple estimates based on the bandgap matching indicate that the efficiency limit in such tandem device is as high as 46%.However,state-of-the-art perovskite/c-Si TSCs only achieve an efficiency of~32.5%,implying significant challenges and also rich opportunities.In this review,we start with the operating mechanism and efficiency limit of TSCs,followed by systematical discussions on wide-bandgap perovskite front cells,interface selective contacts,and electrical interconnection layer,as well as photon management for highly efficient perovskite/c-Si TSCs.We highlight the challenges in this field and provide our understanding of future research directions toward highly efficient and stable large-scale wide-bandgap perovskite front cells for the commercialization of perovskite/c-Si TSCs.

Photon energy loss and management in perovskite solar cells

The power conversion efficiency(PCE)of perovskite solar cells(PSCs)has increased rapidly to 25.7%in 2022.There is growing curiosity about whether it will increase further up to the PCE limit.Understanding the fundamental energy loss mechanism and targeted treatment is the crux to step forward,especially the definite and management of photons in PSCs.Here,we first briefly review the main modes of photon energy loss in PSCs and illustrate the significance of photon recycling.Next,historical research trials to overcome these loss mechanisms in PSCs are highlighted,including the application of anti-reflection coatings,plasmonic strategies,and the adoption of upconversion and downconversion materials.Finally,we make a brief summary and prospect about strategies that can help to improve photon management in the future.

An optical slot-antenna-coupled cavity (SAC) framework towards tunable free-space graphene photonic surfaces

The optical conductivity of single layer graphene (SLG) can be significantly and reversibly modified when the Fermi level is tuned by electrical gating. However, so far this interesting property has rarely been applied to free-space two-dimensional (2D) photonic devices because the surface-incident absolute absorption of SLG is limited to 1%–2%. No significant change in either reflectance or transmittance would be observed even if SLG is made transparent upon gating. To achieve significantly enhanced surface-incident optical absorption in SLG in a device structure that also allows gating, here we embed SLG in an optical slot-antenna-coupled cavity (SAC) framework, simultaneously enhancing SLG absorption by up to 20 times and potentially enabling electrical gating of SLG as a step towards tunable 2D photonic surfaces. This framework synergistically integrates near-field enhancement induced by ultrahigh refractive index semimetal slot-antenna with broadband resonances in visible and infrared regimes, ~ 3 times more effective than a vertical cavity structure alone. An example of this framework consists of self-assembled, close-packed Sn nanodots separated by ~ 10 nm nanogaps on a SLG/SiO2/Al stack, which dramatically increases SLG optical absorption to 10%-25% at λ = 600–1,900 nm. The enhanced SLG absorption spectrum can also be controlled by the insulator thickness. For example, SLG embedded in this framework with a 150 nm-thick SiO2 insulating layer displays a distinctive red color in contrast to its surrounding regions without SLG on the same sample under white light illumination. This opens a potential path towards gate-tunable spectral reflectors. Overall, this work initiates a new approach towards tunable 2D photonic surfaces.

Perfect solar absorber based on nanocone structured surface for high-efficiency solar thermoelectric generators

Nanostructured surface is a promising photon management strategy to tune spectrum in design of the selective solar absorber.In this paper,we propose a nanocone structured surface as a perfect solar absorber in application of the solar thermoelectric generators(STEGs).The trade-off between the solar absorption and the mid-infrared emission is obtained to maximize the STEG efficiency.The effects of the geometric parameters,thermal concentration,incident angle and polarized state as well as the lattice arrangement are systematically investigated.The results show that the STEGs equipped with our proposed selective solar absorber can achieve a peak efficiency of 6.53%under AM1.5G condition(no optical concentration).Furthermore,the selective solar absorber exhibits insensitive behavior to the incident angle and polarization angle as well.This means that the proposed selective solar absorber can utilize solar energy as much as possible and be generally suitable in equipping the STEGs without optical concentration.

Enhancing the Efficiencies of Organic Photovoltaic and Organic Light-Emitting Diode Devices by Regular Nano-Wrinkle Patterns

Organic photovoltaic(OPV) cells and organic light-emitting diodes(OLEDs) are energy harvesting and generation devices that have attracted great attention these years because of their low costs, thin film structures,flexibility and environment-friendly manufacturing processes. For such thin film devices, photon management methods that increase the light absorption of OPV cells and the light extraction from OLEDs are highly desirable.Here, we report the experimental efforts to fabricate geometrically tunable and spontaneously formed nano-wrinkle structures with large areas, and the theoretical results on photon management with the nano-wrinkles.