Regulating Electron-Phonon Coupling by Solid Additive for Efficient Organic Solar Cells.

Strong electron-phonon coupling can hinder exciton transport and induce undesirable non-radiative recombination, resulting in a shortened exciton diffusion distance and constrained exciton dissociation in organic solar cells (OSCs). Therefore, suppressing electron-phonon coupling is crucially important for achieve high-performance OSCs. Here, we employ the solid additive to regulating electron-phonon coupling in OSCs. The planar configuration of SA1 confers a significant advantage in suppressing lattice vibrations in the active layers, reducing the scattering of excitons by phonons caused by lattice vibrations. Consequently, a slow but sustained hole transfer process is identified in the SA1-assisted film, indicating an enhancement in hole transfer efficiency. Prolonged exciton diffusion length and exciton lifetime are achieved in the blend film processed with SA1, attributed to a low non-radiative recombination rate and low energetic disorder for charge carrier transport. As a result, a high efficiency of 20% was achieved for ternary device with a remarkable short-circuit current. This work highlights the important role of suppressing electron-phonon coupling in improving the photovoltaic performance of OSCs.

Amino Acid Double-Passivation-Enhanced Quantum Dot Coupling for High-Efficiency FAPbI3 Perovskite Quantum Dot Solar Cells.

Formamidinium lead triiodide (FAPbI3) perovskite quantum dot has outstanding durability, reasonable carrier lifetime, and long carrier diffusion length for a new generation of highly efficient solar cells. However, ligand engineering is a dilemma because of the highly ionized and dynamic characteristics of quantum dots. To circumvent this issue, herein, we employed a mild solution-phase ligand-exchange approach through adding short-chain amino acids that contain amino and carboxyl groups to modify quantum dots and passivate their surface defects during the purification process. As a result, the photoelectric conversion efficiency of FAPbI3 perovskite quantum dot solar cells (PQDSCs) increased from 11.23 to 12.97% with an open-circuit voltage of 1.09 V, a short-circuit current density of 16.37 mA cm-2, and a filling factor of 72.13%. Furthermore, the stability of the device modified by amino acids retains over 80% of the initial efficiency upon being exposed to 20-30% relative humidity for 240 h of aging treatment. This work may offer an innovative concept and approach for surface ligand treatment to improve the photovoltaic performance of PQDSCs toward large-scale manufacture.

Cosensitized Quantum Dot Solar Cells with Conversion Efficiency over 12.

The improvement of sunlight utilization is a fundamental approach for the construction of high-efficiency quantum-dot-based solar cells (QDSCs). To boost light harvesting, cosensitized photoanodes are fabricated in this work by a sequential deposition of presynthesized Zn-Cu-In-Se (ZCISe) and CdSe quantum dots (QDs) on mesoporous TiO2 films via the control of the interactions between QDs and TiO2 films using 3-mercaptopropionic acid bifunctional linkers. By the synergistic effect of ZCISe-alloyed QDs with a wide light absorption range and CdSe QDs with a high extinction coefficient, the incident photon-to-electron conversion efficiency is significantly improved over single QD-based QDSCs. It is found that the performance of cosensitized photoanodes can be optimized by adjusting the size of CdSe QDs introduced. In combination with titanium mesh supported mesoporous carbon as a counterelectrode and a modified polysulfide solution as an electrolyte, a champion power conversion efficiency up to 12.75% (Voc = 0.752 V, Jsc = 27.39 mA cm-2 , FF = 0.619) is achieved, which is, as far as it is known, the highest efficiency for liquid-junction QD-based solar cells reported.

Investigation of multi-junction solar cells using electrostatic force microscopy methods.

Multi-junction III-V solar cells are designed to have a much broader absorption of the solar spectrum than Si-based or single junctions, thus yield the highest conversion. The conversion efficiency can be further scaled with sun concentration. The ability of high conversion efficiencies makes multi-junction prime candidates for fine-tuning explorations aimed at getting closer to the theoretical efficiencies. In this paper, we report on electrostatic force microscopy (EFM) measurements of the built-in potential of multi-junction III-V semiconductor-based solar cells. Kelvin probe force microscopy (KPFM) was employed to qualitatively study the width and electrical properties of individual junctions, i.e., built-in potential, activity, and thickness of the p-n junctions. In addition, the voltage drops across individual solar cell p-n junctions were measured using Kelvin probe microscopy under various operation conditions: dark; illuminated; short-circuit; and biased. We present a method which enables the measurement of a working structure, while focusing on the electrical characteristics of an individual junction by virtue of selecting the spectral range of the illumination used. We show that these pragmatic studies can provide a feedback to improve photovoltaic device design, particularly of operation under a current mismatched situation. This new analysis technique offers additional insights into behavior of the multi-junction solar cell and shows promise for further progress in this field.