Non-fullerene acceptor (NFA)-based optoelectronic devices have received great research interest because of their unique optoelectronic characteristics like tunable bandgap, strong near-infrared (NIR) light absorption, and enhanced stability. However, the demonstration of a self-powered NIR broadband photodiode with excellent photoresponse and low dark current density comparable to that of commercial inorganic counterpart remains a challenge. Herein, the high-performance solution-processed self-powered organic broadband photodiode is demonstrated by using a narrow bandgap NFA with a low dark current density (J d) of 1.05 nA/cm2 at 0 V. The dark leakage current of the device is greatly improved by adopting a “thick junction” strategy, and the optimized device exhibits a J d of 6.5 nA/cm2 even at a moderate applied bias voltage of −1.5 V. The devices exhibit more than 70% external quantum efficiency in the 550–830 nm wavelength (λ) range and a specific detectivity of 2.65 × 1012 jones at λ ∼ 770 nm under the self-powered mode of operation. The fabricated photodetector is used in photoplethysmography (PPG) measurement, demonstrating its application in real-time heart-rate monitoring and pulse oximetry.

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Molybdenum disulfide (MoS 2 ) is an emerging twodimensional (2D) material for next-generation optoelectronic and energy storage devices. Although various efforts have been made to understand the photocurrent generation mechanisms and to improve the photoresponse behavior of 2D MoS 2 nanosheets (NSs), little is understood about the mechanisms underlying the photocurrent response of few-layer MoS 2 NSs, particularly the fast response of photocurrent followed by a slow rise under pulsed illumination. In this work, we have investigated the mechanisms behind the photoresponse of few-layer MoS 2 NS-based twoterminal devices via time-resolved photocurrent measurements. The photoresponse of such devices under different bias voltages and light intensities is measured and the photocurrent initially shows a fast response in the time scale of ∼95 μs followed by a slow-rise current (SRC) with a rise-time constant of ∼50 s. The photocurrent increases sublinearly with intensity and exponentially with temperature, indicating the presence of traps. This work reports a systematic study of the photocurrent and SRC in few-layer MoS 2 NSs and concludes that the SRC effects can be ascribed to the photobolometric and trap-assisted photogating processes. Besides, this study points out a correlation of the SRC in MoS 2 with the temperature and vacuum level.

Uniform and high-electronic-quality perovskite thin films are necessary for high efficiency perovskite solar cells (PSCs) and additives play a major role in improving the quality of the perovskite films. Here, we demonstrate acetylammonium chloride (AAC) as an additive to effectively control the morphology and crystal quality of the methylammonium lead iodide perovskite film. AAC incorporated PSCs have shown an improved power conversion efficiency (PCE) of 15.9% compared to 14.9% of the control device. Furthermore, AAC incorporated PSCs exhibit high operational stability by retaining 89% of the initial efficiency after 150 hours of continuous operation while the control devices degrade to 51% of the initial PCE in just 45 hours. The improved performance and stability of the AAC incorporated PSCs can be attributed to the (1) formation of uniform sized perovskite films of larger grains and (2) passivation of defects present in the grain boundaries and surfaces of the perovskite film. The defect density has reduced from 4.1x1016 cm-3 to 1.97x1016 cm-3 on addition of AAC to the perovskite film. The reduction in defects-induced non-radiative recombination decay pathways, as further verified from impedance and capacitance-frequency measurements, has caused an enhancement in the open circuit voltage of the AAC incorporated devices and thus an improvement in the PCE and stability of the devices.

The introduction of a third component vehemently modifies the morphology and charge carrier dynamics in the blend of a donor-acceptor pair, thereby affecting the photovoltaic properties of organic solar cells (OSCs). Combining steady-state, impedance, and transient spectroscopic measurements, photovoltaic properties of 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (DIB SQ) incorporated additive-free PTB7:PC70BM OSCs are assessed. As observed from steady-state measurements, concomitant enhancement in open-circuit voltage and short-circuit current has caused 33% enhancement in power conversion efficiency with good reliablity and reproducibility. On introducing 25 wt.% SQ to the OSCs, VOC has increased from 0.74 to 0.80 V while JSC has improved from 11.3 to 13.9 mAcm-2 with an increment in exciton dissociation probability rate from 81.5% to 94.9%. However, the fill factor values show inconsistent marginal variations with SQ addition. Equivalent circuit modeling of bias-voltage dependent impedance spectra along with transient photovoltage measurements reveal an improvement in effective charge carrier lifetime for the SQ incorporated OSCs, in comparison to the binary device. The addition of SQ also ensures better charge transport and extraction, as evidenced from photo-CELIV and transient photocurrent analysis. Atomic force microscopic (AFM) images confirm effective tuning of the morphology of the active layer when SQ is introduced into the binary blend, favoring efficient charge dissociation and transport. The possible operation mechanism of SQ incorporated ternary OSCs is proposed based on photoluminescence and AFM measurements. Moreover, the un-encapsulated OSC with 25 wt.% SQ has retained 91% of the initial PCE, while for the binary device, the PCE has declined to ~ 75% of the initial value after 200 hours of continous 1 sun illumination from a white LED in ambient atmosphere.