Among the photovoltaic technologies, polymer solar cells and perovskite solar cells are among the most promising due to lower production costs and ease of fabrication. Conjugated p-type copolymers are a key component in polymer solar cells as photon absorbers along with n-type acceptors.
Acknowledgements
I express my sincere thanks to my friends Tousif, Atikur, Papai, Imran, Habibur, Pritam, Talha, Hasan, Rukhsar, Huzaifa, Anam, Sanavil, Furqan bhai, Abid, Suhail bhai, Shahab bhai, Aslam, Alim, Saddam, Ishtiyak , and other friends for their constant unfailing support, their encouragement and all the help they provided whenever needed. I am also grateful to my sisters and brother for their eternal love, cooperation and emotional support which was desperately needed to complete this work.
List of Tables
Greener Energy Technology as the Solution of Global Warming
Introduction
This has emerged as the primary concern of human society, which has also created a global consensus to promote alternative energy sources such as wind, hydro, geothermal, biomass and solar energy. Among these sources, solar technology has emerged as the most prominent and sustainable choice that has the potential to meet global demands.
Polymer and Perovskite Solar Cells
In contrast, the photovoltaic technologies such as polymer solar cells (PSCs) and perovskite solar cells (PVSCs) are clearly advantageous compared to silicon-based inorganic solar cells. As a photon-absorbing layer, perovskite materials meet almost all criteria to meet the performance of silicon-based inorganic solar cells.
Device Architecture and Working Principle .1 Polymer Solar Cells
- Perovskite Solar Cells
Perovskite materials based on organometallic halides have emerged over the past decade as the most prominent light-absorbing material for solar cells. The planar devices can be fabricated by following the following (n-i-p)/inverted (p-i-n) configuration depending on the type of contact (n-type or p-type, respectively) included towards the transparent electrode (Figure 1.3b-c ).20-21 .
Constituents of Polymer and Perovskite Solar Cells .1 Transparent Conducting Electrode
- Electron Transporting Layer (ETL)
- Active Layer
- Hole Transporting Layer
- Metal Electrode
Suppressing defects and modulating the grain size of the active layer can be effective in mitigating charge carrier recombination. Additionally, interfacial layers are often used in both PSCs and PVSCs to modulate the work function level of the metal electrode and improve charge transport in the device.
Device Measurements .1 J-V Characterization
- External Quantum Efficiency (EQE)
- Impedance Spectroscopy Measurements
The duty factor is a device parameter used to estimate the deviation of the actual efficiency of a solar cell from the maximum theoretically expected power output. EQE is the ratio between the number of charge carriers collected by the solar cell and the number of photon energy incident on the solar cell (Figure 1.6).
Active Layer Engineering in Polymer and Perovskite Solar cell
- Active Material Engineering for PSCs
- Development of Donor Copolymers
- Donor Terpolymers
- Materials for Perovskite Solar Cells
Lewis bases, such as thiophene, pyridine and pyrazine were also included as additives to soften the defect states in photoactive layer.63,64 The passivation of perovskite layer significantly reduced the non-radiative recombination and significantly improved the performance of the PVSCs. The instability of PVSCs under ambient condition is a major obstacle to its commercial viability. The presence of FBZ significantly improved the molecular alignment of the polymer in thin film by significantly reducing the dihedral angle in the polymer backbone.
A brief summary of research work that has been done and possibilities of investigations that are essential for the practical application of photovoltaic devices in the near future is also presented. Adjust the open circuit voltage by incorporating difluorophenyl unit in polymer backbone to achieve high efficiency polymer solar cells. The incorporation of the FBZ monomer into polymer backbone has been demonstrated as a very effective method to synthesize cost-effective donor polymers to fabricate high performance PSCs with improved VOC.
Introduction
The hole and electron mobility of the active polymer layers were also estimated using the Space Charge Limited Current (SCLC) method. There are reports in which non-covalent conformational locking (S⋯F, OF⋯F, or C⋯F) is used to synthesize semi-crystalline polymers, where these interactions have improved the intermolecular orderly packing and flatness of the polymer backbone.27–29 . The presence of FBZ significantly improved the molecular alignment of the polymer in thin film by reducing the dihedral angles between the monomers.
Results and discussion
Synthesis of polymers (PTB7-Th, M1, and M1´)
Nevertheless, there is a blue shift in the UV-visible spectra for M1 and M1′ due to weaker FBZ acceptance. The absorption of M1 and M1' in the 300–650 nm range had a higher intensity compared to PTB7-Th. A significant positive shift in the oxidation potential (Eox) was observed for the terpolymers with increasing percentage of FBZ incorporation.
LUMOHOMOTop ViewSide View
Conclusion
Two random terpolymers M1′ and M1′ were synthesized incorporating 5% and 10% of the FBZ unit in the polymer backbone, with PTB7-Th being synthesized as a reference. Incorporation of the FBZ unit into the polymer backbone resulted in a significant change in the opto-electronic. The improvement of SHA and VOC collectively contributed to the increase of PCE from 7.87% for PTB7-Th to 8.78% for M1.
Experimental Section .1 Materials
- Instruments
- General Synthesis Procedure
- Device Fabrication
A significant enhancement of SHA by 11% (from 15.57 mA/cm2 for PTB7-Th to 16.62 mA/cm2 for M1) was also observed, which is attributed to the increased charge carrier mobility of the films of thin, as confirmed by SCLC measurements. The XRD patterns of the perovskite films were studied using a Rigaku Micromax-007HF diffractometer equipped with Cu Kα1 radiation (λ = 1.54184 Å). To further calculate the electron mobility of the polymers, the architecture of ITO/ZnO/polymers:PC71BM/Ca/Al was used.37 The slope value was ∼2 for all SCLC plots.
PCE=9.48% PCE=8.13%
PCE=8.80%
Introduction
In addition, various strategies such as novel monomer incorporation, side-chain alteration, functional group modifications and novel fabrication methods have been used to improve the efficiency and environmental stability of PSCs.11-17. The structural modification of the polymer backbone can be used as an efficient method to improve the environmental stability of PSCs along with its PCE.15 The incorporation of an appropriate third monomer into the D-A copolymer backbone can be used as an effective strategy to improve the morphology of mixing film . The incorporation of FPM can induce varied non-covalent interactions (sulfur-fluorine, hydrogen-fluorine, or oxygen-fluorine) that can provide conformational lock in the polymer backbone and result in a reduced dihedral angle.23,24 The non-covalent interactions can significantly better charge carrier movement to improve the short-circuit current density (JSC) of PSCs.
Results and Discussion
A box plot for various photovoltaic parameters is included for all polymer blends in Figure 3.4a-d, which also represents the reproducibility of these PSCs. To gain a better insight into interfacial charge carrier kinetics and recombination, electrochemical impedance spectroscopy (EIS) was analyzed for all polymer blends under dark conditions (Figure 3.5c). To understand the reasons for the sharp decrease in JSC after ambient exposure to PTB7-Th, we analyzed the change in the absorption profile of the PTB7-Th:PC71BM blend along with other polymer blends for 1000 hours at ambient conditions (Figure 3.7 a-d).
Conclusion
Higher JSC was achieved for M1 and M2 based blend due to its low dihedral angle and uniformly separated phase with nano-morphology. In contrast, due to the lower absorption at NIR region and relatively poor blend morphology of M3 blend, it showed overall lower photovoltaic performance. This improvement of JSC and VOC collectively improved the PCE for M1 and M2 based blend to 9.48% and 8.80% respectively.
Experimental Section .1 Materials
- Instruments
- General Synthesis Procedure
- Device fabrication
To determine the oxidation potential of polymers, three electrodes were used and a polymer film was coated on a glassy carbon electrode. Newport, Oriel Sol 3A solar simulator with an Oriel 500 W xenon lamp connected to AM 1.5 Globe filter was used as solar cell characterization. PSCs were fabricated with the conventional architecture of ITO/PEDOT:PSS/Active layer blend/BCP/Silver.
TFA FA
Passivation Enhanced
Hydrophobicity
- Introduction
- Results and discussion
- Conclusion
- Experimental Section .1 Materials
- NiO x Film Preparation
- Device Fabrication
- Device Characterization
- References
To further investigate the effect of PFA, UV-visible spectra of thin films passivated with varied concentration of PFA were analyzed (Figure 4.3a). In Figure 4.4c, a histogram (of 15 devices) is shown for the PCE of PFA-based devices showing improved efficiency with better reproducibility than the pristine devices. The series resistance (RS), recombination resistance (Rrec) and capacitance (C) can be determined for pristine and PFA-based devices from the fitted graph (using corresponding circuit in inset) as shown in Figure 4.8c.
Voltage, V
Traps Passivation of P erovskite
Introduction
Herein, a multifunctional additive, 5-fluoropyrimidine-2,4(1H,3H)-dione (FPD) is used to suppress the wide range of defects and modulate the microstructures of perovskite films. The presence of a fluorine atom also contributed to increase the hydrophobicity of perovskite thin films, significantly limiting moisture penetration into the perovskite layer under ambient conditions. This can be attributed to the effective passivation of multifunctional FPD to suppress defects and increase the hydrophobicity of the perovskite surface.
Results and discussion
To further evaluate the photo-responsive nature of FPD-passivated PVSCs, steady-state current measurements at maximum power point were analyzed (Figure 5.2f). To further analyze the impact of passivation on absorption profile, UV-vis absorption spectra were recorded for perovskite thin films passivated by varied concentrations of FPD (Figure 5.4a). To elucidate the passivation effect on the crystalline nature of perovskite film, X-ray diffraction (XRD) was analyzed for thin films passivated with varied concentrations of FPD (Figure 5.4b).
2degree
Conclusions
In summary, we illustrated the impact of incorporating multifunctional additive molecule FPD into perovskite photoactive layer that significantly regulated the optoelectronic property, surface morphology and reduced defects in perovskite lattice structure. The traps and the defect density in perovskite active layer are significantly suppressed due to the strong interaction between functional groups of FPD and perovskite crystal lattice. Thus, this FPD passivation approach confirmed that it is an efficient method to improve the PCE along with the long-term stability of PVSCs to withstand adverse humid conditions.
Experimental Section .1 Materials
- NiO x Film Preparation
- Device Fabrication
- Device Characterization
For the passivated device, different concentrations (1.5 mg/ml to 4.5 mg/ml) of FPD were added to the precursor solution. Then, for both passivated and pristine devices, 12 mg/mL PC61BM solution was coated as electron transporting layer (ETL) at 1200 rpm and re-annealed at 80 °C for 5 min on a hot plate. Then a thin layer of Rhodamine 101 inner salt was spin-coated at 4000 rpm from a solution of 0.5 mg/ml in IPA.
PSCs
PVSCsA
Conclusions
In the third chapter, a comparative study was performed on the impact of three fluoroarenes (2,5-difluorobenzene, 2,3-difluorobenzene, and 2,3,5,6-tetrafluorobenzene) by incorporating them into PTB7-Th backbone. Fourth Chapter focused on the capture passivation of MAPbI3-based solar cells by fluoroarene derivatives. An insight into the crystallization, morphology, charge carrier dynamics and trap softening of perovskite layer was provided.
Future prospects
The environmental stability of perovskite materials can be improved by introducing hydrophobic additives or by preparing 2D/3D mixed perovskite by incorporating larger organic cations. Further study to understand Sn-based perovskites may lead to the progress in the performance and stability of Sn-based PVSCs. The aim of these approaches was to improve the photovoltaic performance and stability of the device.
Maimur Hossain
Ritesh Kant Gupta, Rabindranath Garai, Maimur Hossain, Mohammad Adil Afroz, Dibashmoni Kalita and Parameswar Krishnan Iyer, "Engineering Polymer Solar Cells: Advances in Active Layer Thickness and Morphology", J. Rabindranath Garai, Ritesh Kant Gupta, Maimur Hossain and Parameswar Krishnan Iyer, Surface-Recrystallized Stable 2D-3D Sorted Perovskite Solar Cells for Efficiency Above 21%", J. Chandan Dawo, Maimur Hossain, Parameswar Krishnan Iyer and Harsh Chaturvedi "Caesium Halide Modified TiO2 for High Performance Dye-Sensitized Solar Cells", (manuscript in preparation).
