The emergence of nonfullerene small-molecule acceptors
(NFSMA)
with the advantages of synthetic versatility, high absorption coefficient
in wide wavelength range, and high thermal stability has attained
the power conversion efficiency (PCE) exceeding 19% for resulted organic
solar cells (OSCs) with the optimization of interface engineering
and active layer morphology. Interfacial layers including both hole
transporting layer (HTL) and electron transporting layer (ETL) are
equally important in the OSCs for facilitating electron and hole extraction
from the bulk heterojunction (BHJ) photoactive layer by the respective
electrodes. In this Review, we summarize the recent progress in the
materials used as HTL and ETL in conventional and inverted OSCs on
the basis of their effect on the PCE. Finally, the prospects of HTL
and ETL materials for NFSMA-OSCs will be provided.
This article presents recent advances in the ternary organic solar cell (TOSC), such as technological interventions from the material design to the device performance, which led to more than 19% power conversion efficiency (PCE). The research and development in TOSCs reported in the past decade have been inspiring and promising in terms of molecular processing to device properties for low-power devices and building integrated photovoltaics applications. Many of these are still in the early phase, enabling researchers to explore more and flourish. The research community has made numerous efforts to address the different aspects to enhance the efficiency and stability of the TOSCs. Therefore, the objective of this article is to review the recent advances in TOSCs and present a comprehensive discussion in this regard. This review also identifies and suggests the possible outlook for the critical issues associated with TOSCs, along with future perspectives.
Understanding the linear and nonlinear optical responses of two-dimensional nanomaterials is essential to effectively utilize them in various optoelectronic applications. Here, few-layer MoS2 and WS2 nanoflakes with lateral size less than 200 nm were prepared by liquid-phase exfoliation, and their linear and nonlinear optical responses were studied simultaneously using experimental measurements and theoretical simulations. Finite-difference time-domain (FDTD) simulations confirmed the redshift in the excitonic transitions when the thickness was increased above 10 nm indicating the layer-number dependent bandgap of nanoflakes. WS2 nanoflakes exhibited around 5 times higher absorption to scattering cross-section ratio than MoS2 nanoflakes at various wavelengths. Open aperture Z scan analysis of both the MoS2 and WS2 nanoflakes using 532 nm nanosecond laser pulses reveals strong nonlinear absorption activity with effective nonlinear absorption coefficient (βeff) of 120 cm/GW and 180 cm/GW, respectively, which was attributed to the combined contributions of ground, singlet excited and triplet excited state absorption. FDTD simulation results also showed the signature of strong absorption density of few layer nanoflakes which may be account for their excellent nonlinear optical characteristics. Optical limiting threshold values of MoS2 and WS2 nanoflakes were obtained as ~ 1.96 J/cm2 and 0.88 J/cm2, respectively, which is better than many of the reported values. Intensity dependent switching from saturable absorption to reverse saturable absorption was also observed for MoS2 nanoflakes when the laser intensity increased from 0.14 GW/cm2to 0.27 GW/cm2. The present study provides valuable information to improve the selection of two-dimensional nanomaterials for the design of highly efficient linear and nonlinear optoelectronic devices.
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