Plasmon-induced trap filling at grain boundaries in perovskite solar cells

Construction Au/FAPbI3 Schottky Heterojunction towards a High-Speed Electron Transfer Channel for High-Performance Perovskite Quantum Dot Solar Cells

Formamidinium lead triiodide quantum dot (FAPbI3 QD) exhibits substantial potential in solar cells due to its suitable band gap, extended carrier lifetime, and superior phase stability. However, despite great attempts toward reconfiguring the surface chemical environment of FAPbI3 QDs, achieving the optimal efficiency of charge carrier extraction and transfer in cells remains a challenge. To circumvent this problem, we selectively introduced Au/FAPbI3 Schottky heterojunctions by reducing Au+ to Au0 and subsequently anchoring them on the surface of FAPbI3 QDs, which acts as a light-harvesting layer and establishes high-speed electron transfer channels (Au dot ↔ Au dot). As a result, the champion photoelectric conversion efficiency of solar cells reached 13.68%, a significant improvement over 11.19% of that of FAPbI3-based solar cells. The enhancement is attributed to efficient and directed electron transfer as well as a more aligned energy level arrangement. This work constructed Au/FAPbI3 QD Schottky heterojunctions, providing a viable strategy to enhance QD electron coupling for high-performance optoelectronic applications.

New Nanophotonics Approaches for Enhancing the Efficiency and Stability of Perovskite Solar Cells

Over the past decade, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has experienced a remarkable ascent, soaring from 3.8% in 2009 to a remarkable record of 26.1% in 2023. Many recent approaches for improving PSC performance employ nanophotonic technologies, from light harvesting and thermal management to the manipulation of charge carrier dynamics. Plasmonic nanoparticles and arrayed dielectric nanostructures have been applied to tailor the light absorption, scattering, and conversion, as well as the heat dissipation within PSCs to improve their PCE and operational stability. In this review, it is begin with a concise introduction to define the realm of nanophotonics by focusing on the nanoscale interactions between light and surface plasmons or dielectric photonic structures. Prevailing strategies that utilize resonance-enhanced light-matter interactions for boosting the PCE and stability of PSCs from light trapping, carrier transportation, and thermal management perspectives are then elaborated, and the resultant practical applications, such as semitransparent photovoltaics, colored PSCs, and smart perovskite windows are discussed. Finally, the state-of-the-art nanophotonic paradigms in PSCs are reviewed, and the benefits of these approaches in improving the aesthetic effects and energy-saving character of PSC-integrated buildings are highlighted.

Organic Semiconductor Based on N, S-Containing Crown Ether Enabling Efficient and Stable Perovskite Solar Cells

The uncoordinated lead cations are ubiquitous in perovskite films and severely affect the efficiency and stability of perovskite solar cells (PSCs). In this work, 15-crown-5 with various heteroatoms are connected to the organic semiconductor carbazole diphenylamine, and two new compounds, CDT-S and CDT-N, are developed to modify the Pb2+ defects in perovskite films through the anti-solvent method. Apart from the oxygen atoms, there are also N atoms on crown ether ring in CDT-N, and both S and N heteroatoms in CDT-S. The heteroatoms enhance the interaction between the crown ether-based semiconductors and the undercoordinated Pb2+ defect in perovskite. Particularly, the stronger interaction between S atoms and Pb2+ further enhances the defect passivation effect of CDT-S than CDT-N, thereby more effectively suppressing the non-radiative recombination of charge carriers. Finally, the efficiency of the device treated with CDT-S is up to 23.05 %. Moreover, the unencapsulated device based on CDT-S maintained 90.5 % of the initial efficiency after being stored under dark conditions for 1000 hours, demonstrating good long-term stability. Our work demonstrates that crown ethers are promising in perovskite solar cells, and the crown ether containing multiple heteroatoms could effectively improve both efficiency and stability of devices.

Break through the Steric Hindrance of Ionic Liquids with Carbon Quantum Dots to Achieve Efficient and Stable Perovskite Solar Cells

Overcoming the negative impact of residual ionic liquids (ILs) on perovskite films based on an in-depth understanding of chemical interactions between ionic liquids and preparing perovskite precursor solutions is a great challenge when aiming to simultaneously achieve long-term stability and high efficiency within IL-based perovskite solar cells (PSCs). Herein, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), a type of IL, was introduced into the perovskite precursor solution, and carbon quantum dots (CQDs) were further introduced into the antisolvent to enhance the photovoltaic properties of PSCs. Both ILs and CQDs synergistically manipulate the crystallization process and passivate defects to obtain high-quality perovskite films. Besides serving as passivation sites to strengthen the collaboration between additives and perovskite materials, the cointroduction of CQDs further promotes the carrier transport process since it not only provides carrier channels at grain boundaries but also forms better energy alignment, which effectively overcomes the charge transfer loss caused by the steric hindrance of ILs. Based on such a synergistic effect of ILs and CQDs, the n-i-p MAPbI3-based PSCs achieve the highest efficiency of 20.84% with improved stability. This simple and low-cost synergistic integration method will subsequently provide direction for optimizing ILs to improve the photovoltaic performance of PSCs.

Buried-Interface Engineering of Conformal 2D/3D Perovskite Heterojunction for Efficient Perovskite/Silicon Tandem Solar Cells on Industrially Textured Silicon

Exploring strategies to control the crystallization and modulate interfacial properties for high-quality perovskite film on industry-relevant textured crystalline silicon solar cells is highly valued in the perovskite/silicon tandem photovoltaics community. The formation of a 2D/3D perovskite heterojunction is widely employed to passivate defects and suppress ion migration in the film surface of perovskite solar cells. However, realizing solution-processed heterostructures at the buried interface faces solvent incompatibilities with the challenge of underlying-layer disruption, and texture incompatibilities with the challenge of uneven coverage. Here, a hybrid two-step deposition method is used to prepare robust 2D perovskites with cross-linkable ligands underneath the 3D perovskite. This structurally coherent interlayer benefits by way of preferred crystal growth of strain-free and uniform upper perovskite, inhibits interfacial defect-induced instability and recombination, and promotes charge-carrier extraction with ideal energy-level alignment. The broad applicability of the bottom-contact heterostructure for different textured substrates with conformal coverage and various precursor solutions with intact properties free of erosion are demonstrated. With this buried interface engineering strategy, the resulting perovskite/silicon tandem cells, based on industrially textured Czochralski (CZ) silicon, achieve a certified efficiency of 28.4% (1.0 cm2 ), while retaining 89% of the initial PCE after over 1000 h operation.

Ultrabroadband hot-hole photodetector based on ultrathin gold film

Hot carriers injected into semiconductor enables below-bandgap photodetection, thus attracting increasing interest. The performance of hot carrier-based device is directly related to the absorptivity of metal. Several strategies such as surface plasmons, metamaterials, and optical cavities are utilized to enhance the weak intrinsic absorption of the metal. However, the detection range is limited by their narrow resonance bandwidth alternatively. Impedance-matched absorbers, whose sheet resistance is equal to half of the free-space impedance (188 Ω), can achieve a wavelength-independent absorptivity up to 50%. Herein, we theoretically design a purely planar hot-hole photodetector based on ultrathin gold film, a new type of metallic impedance-matched absorber. Benefiting both from the efficient absorption and ultrathin nature of the film, we predict that the photoresponsivity of our device can reach 35.7 mA W^-1 under zero bias at the wavelength of 1.3 μm, with a full width at half maximum (FWHM) of detection range reaching 1050 nm, setting a new record for the bandwidth of the hot carrier photodetectors. We also demonstrated that the device is robust to the incident angle and can be tuned through the external bias voltage. This work provides a pathway for broadband hot carrier detectors and other hot carrier-based applications.

Highly flexible organo-metal halide perovskite solar cells based on silver nanowire-polymer hybrid electrodes

Flexible perovskite solar cells (FPSCs) have attracted considerable attention due to their broad application possibilities in next generation electronics. However, the commonly used transparent conductive electrodes (TCEs), such as indium tin oxide (ITO), suffer from poor flexible performance, impeding the development of FPSCs. Here, we propose a hybrid electrode (PUA/AgNWs/PH1000) comprising a thin percolation network of silver nanowires (AgNWs) inlaid on the surface of a flexible substrate (PUA) modified with a conductive layer (PH1000), which exhibits high optical transmittance and electrical conductivity, as well as robust mechanical flexibility. By applying the proposed PUA/AgNWs/PH1000 hybrid electrode in FPSCs, the resulting ITO-free devices exhibit the desired flexibility and mechanical stability; it can survive repeated continuous bending cycles and retain 77.4% of its initial power conversion efficiency after 10 000 bending cycles with the bending radius of 5 mm.

Further Boosting Solar Cell Performance via Bandgap-Graded Ag Doping in Cu2ZnSn(S,Se)4 Solar Cells Compared to Uniform Ag Doping

Cu₂ZnSn(S,Se)₄ (CZTSSe) is a hopeful substitution to commercialized Cu(In,Ga)Se₂ (CIGSe) devices with similar structure and optoelectronic properties and has advantages of nontoxicity, low cost, and abundant reserves. However, the traditional flat bandgap structure of the CZTSSe absorber layer does not efficiently enhance the collection of photogenerated electrons and decrease recombination. Graded bandgap engineering toward the interfaces of CIGSe solar cells is the key to realize high-efficiency devices. In this study, we obtained (Cu_1-xAg_x)₂ZnSn(S,Se)₄ (CAZTSSe) absorber layers with high-concentration Ag doping at both ends of the absorption layer and undoped or low-concentration Ag doping in the middle part through a new miscible layered precursor method. This bandgap structure suppressed Cu_Zn defects, delayed Fermi level pinning near the CZTSSe/CdS interface, sustained good electrical conductivity and light absorption in the middle of the absorption layer, improved the conversion efficiency of incident light, and inhibited recombination of carriers toward the Mo back electrode. In addition, we also compared the performance of undoped, uniformly Ag-doped, and V-type Ag-doped CZTSSe devices to acquire a deeper understanding of the reasons for the enhanced performance. It can be found that compared with undoping, the open-circuit voltage (V_oc) of the best devices with uniform doping (x = 15%) increased from 379 to 386 mV, the fill factor (FF) increased from 44.70 to 54.14%, and the photoelectric conversion efficiency (PCE) increased from 4.63 to 6.21%. More surprisingly, the V_oc of the optimal CAZTSSe devices (sample D) with Ag-graded doping was increased to 413 mV and the FF was increased to 59.63%. It also achieved an impressive PCE of 7.35%. The above results prove the importance of tuning Ag gradient doping of CZTSSe films for improving solar cell performance.

Morphology and Luminescence Regulation for CsPbBr3 Perovskite Light-Emitting Diodes by Controlling Growth of Low-Dimensional Phases

At present, the high defect density and strong nonradiative recombination rate of all-inorganic cesium lead bromide (CsPbBr₃) perovskite light-emitting diodes (PeLEDs) seriously inhibit the improvement of their quantum efficiency. In this paper, the addition of a short-chain additive, diethylammonium bromide (DEABr), aims to control the generation of a quasi-2D large n-phase to optimize the surface morphology and construct two-dimensional/three-dimensional (2D/3D) heterojunction perovskite structures to enhance the EL efficiency of PeLEDs. Through Kelvin probe force microscopy (KPFM) characterization, we confirmed that the 2D phase grains with a low potential are locally formed on the surface of the perovskite film under the action of DEABr. The existence of the 2D phase effectively improved the surface morphology and suppressed surface defects. In addition, the in situ constructed 2D/3D heterojunction perovskite structure further increases the exciton radiative recombination rate and significantly improves the electroluminescent performance. By optimizing its doping concentration, the optimal all-inorganic PeLED displays a current efficiency (CE) of 30.3 cd A^-1, an external quantum efficiency (EQE) of 9.6%, and a maximum brightness of 32,500 cd m^-2. According to our results, the formation of 2D structures on the surface of the CsPbBr₃ film can improve surface morphology issues and optoelectronic properties of the film.