We have addressed the reviewers' concerns as stated in the decision letter for our previous submission. A detailed summary of the comments and the actions taken to address them are included at the end of this document. This article discusses different types of photovoltaic and hybrid systems with nanogenerators, their evolution since their conception in 2009 and the current state of technology.
A discussion of the common use cases for each type of nanogenerator is included in these sections. While most of the works reviewed in the manuscript have used the stacked structure for the integration of hybrid devices, they vary considerably in how the integration has been achieved. It will benefit the readers if the choice of the figure can be expanded, such as power output curves, diagrams of working mechanism.
SC power generation is affected by several factors such as radiation intensity, spectral bandwidth of the incident radiation, and the inability to generate power at night. Due to the reasons described earlier regarding the high compatibility of photovoltaic technologies with nanogenerators together with the ever-increasing interest in this field evidenced by the increasing trend of publications, a work summarizing the current status of HCs is essential. PV-NG. The technical and numerical aspects of all the articles discussed are summarized in a table at the end of the article.
The final section discusses the current status of PV-NG HCs and potential vectors for the development of these devices.
Nanogenerators and Solar cells – Types and Fundamentals 1 Piezoelectric and Triboelectric Nanogenerators
The relative propensity of triboelectric materials to become electrically charged during contact with another triboelectric material is classified according to the intensity and polarity of the charges developed in the array, called the triboelectric array . TENG contact separation method – two triboelectric materials are separated by a distance and charges are induced between them upon contact due to an external force. These charges cause an electrical potential to develop between two electrodes, each attached to one of the triboelectric materials, when there is a gap between the two bodies.
TENG relative sliding mode - opposite charges are induced in triboelectric materials when they slide laterally along each other due to polarization. This results in a net movement of electrons along the electrodes connected to the triboelectric materials to balance the charges, resulting in an alternating current output. The generated current varies according to periodic changes in the relative distance between the bodies.
Free standing mode - in this type of TENG two triboelectric materials are connected via electrodes and fixed with a small gap between each other so that there is no relative movement between them. This change corresponds to the change in research efforts in the nanogenerator itself – TENGs have a greater share of research interest due to the countless potential applications, the identification of new triboelectric materials and device structures, and the larger modes and flexibility of operation compared to PENGs. 10,11].
- Dye Sensitized solar cells (DSSC)
- Amorphous(α) Si solar cells
- Quantum Dot Sensitized Solar cell (QDSSC)
- Bulk Heterojunction Polymer Solar cells
PENG and TENG were equally employed in PV-NG HC until 2014, when interest in the use of PENG declined sharply. The use of TENGs and PENGs in hybrid PV-NG devices was presented in Section 3. Based on the end use and desired properties, PV-NG HCs have been developed along two paths – rigid and flexible devices.
The proposed applications for rigid HCs consist of large-scale static installations—the kind most commonly observed with conventional silicon-based SC panel installations. In this type of HC, the nanogenerator serves to enhance or supplement the function of the SC, which remains the primary power producer. This section of the article provides a summary of the four SC types observed in PV-NG HCs.
Si amorphous solar cells use thin films of silicon deposited from precursor gases via chemical vapor deposition processes. Thin films deposited in this way are amorphous in nature and consist of multiple dangling bonds in their microstructure, which lowers the band gap energy of α-Si compared to crystalline Si. The properties of the nanocrystals can be fine-tuned to achieve desired bandgap energy values to ensure optimal energy conversion with minimal loss.
The flexibility also allows QDDSCs to be used to harvest energy from a wide range of the solar spectrum. However, it is still somewhat lacking compared to conventional single-junction semiconductor solar cells . BHPSCs are a class of solar cells that consist of a polymer-based active layer sandwiched between two contacts.
The bulk heterojunction construction is adopted to provide the maximum possible interfacial area between the donor and acceptor materials, thereby maximizing charge separation. BHPSCs are lightweight and cheaper and easier to manufacture via solution processing than conventional solar cells. Also, the flexible nature of the polymer-based active layer can be exploited to produce flexible solar cells .
PV-NG Hybrid Cells
- DSSC and Nanogenerator Hybrid Cells
- QDSSC and Nanogenerator Hybrid Cells
- BHPSC and Nanogenerator Hybrid Cells
- Si-Solar cell and Nanogenerator Hybrid Cells
- Perovskites and their role in Nanogenerators and PV-NG Hybrids
The HC structure was a back-to-back sandwich of the DSSC and PENG, as observed in previous works. A 6% increase in the optimal power of the HC was reported due to the contribution of the NG operating together with the DSSC. It was observed that the output of the tissue TENG was a direct function of the momentum of the tissue.
The optimization of the energy harvesting circuit was proposed as a potential area of interest to better utilize the output of the HC. The output of the HC was used to drive an IR sensor for IoT applications, demonstrating its potential as a self-sustaining power source. It was reported that the NG output increased the voltage of the HC by a factor of 2, while the energy conversion efficiency was 1.5%.
A rectifier circuit was used to convert the AC output of the NG and the devices were connected in parallel. A silver nanowire (Ag NW)/polyimide (PI) composite electrode was used to improve the transparency and flexibility of the S-TENG and reduce any barriers to OSC operation. This resulted in a 16% increase in SC PCE, while the HC became resistant to surface contamination due to the self-cleaning property of the GHF.
The inclusion of the GHF also improved the voltage and current outputs of the TENG by 120% and 105%. The use of the varied material properties of a single substance (PVDF) to extract energy from multiple sources (heat, pressure) has been demonstrated by this class of hybrid cells . The self-cleaning properties of the MM-TENG helped maintain the SC's long-term operational efficiency.
A new switching circuit coupled with a rectifier was developed to convert and store the HC output. A transformer was used for the TENG output for impedance matching with the SC output reducing the impedance of the TENG. The application of HC as an IoT-based active weather sensor was demonstrated.
They observed that the TENG extends the energy harvesting period of the HC while having no adverse effects on the SC. Another implementation of a perovskite-nanogenerator hybrid device was the work of Zhang et al. .
Summary and recommendations for future work
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