Organic phototransistors (OPTs) can enable essential applications, such as nonvolatile memory, artificial synapses, and photosensors in next-generation optical communication and wearable electronics. Among these applications, nonvolatile OPT memories are particularly promising, as they can retain captured visual information for extended periods, making them valuable for data storage, image and video processing applications. The capability of storing multi-bit information, which provides a low-cost way to increase the memory density per unit cell area, is one of the most critical challenges of memory products. In this work, we explore different solution-processible electrets to obtain highly sensitive phototransistor memory devices. Different planar heterojunctions, including small molecule/small molecule and small molecule/polymer, are used to fabricate OPT memories. Additionally, we explore the feasibility of producing polymer/polymer planar heterojunctions through printing processes. Firstly, OPT memories that can be programmed with white light and erased by applying a negative voltage are fabricated with a planar heterojunction of a nonconductive nanographene layer and a semiconducting layer of 2,9-didecyldinaphtho[2,3-b:2’,3’-f]thieno[3,2-b]thiophene (C10-DNTT). We systematically study the optical and memory characteristics of devices with an 8 nm nanographene (NG) layer. The photosensitivity of such devices can be as high as 3.4×105. The memory also shows quite good endurance and data-storing stability; an endurance of 100 write-read-erase-read (WRER) cycles and 1.5×105 s retention time are obtained. The thickness of the NG layer has a considerable influence on the performance of fabricated devices. The results suggest that devices with a thicker NG layer are more sensitive to weak light. In comparison, devices with a relatively thin NG layer are found to be promising for multi-bit photo memory devices. Secondly, we fabricate OPT memories by replacing the nanographene layer with a commercially available semiconducting polymer, namely Poly(2,5-bis(2-octyldodecyl)-3,6-di(pyridin-2-yl)-pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-2,2’-bithiophene) (PDBPyBT). This polymer possesses a narrow bandgap and exhibits a broad range of light absorption, spanning from ultraviolet (UV) to red light wavelengths. As a result, the fabricated devices are capable of responding to a broad spectrum of light colors. The light response of these devices is investigated in terms of their reaction to different colors of light. Also, devices with varying thicknesses of the PDBPyBT layer are fabricated and studied. The results indicate that all of the fabricated devices demonstrate multi-bit programming properties, and the devices incorporating a thin, ribbon-structured PDBPyBT layer are particularly well-suited for applications as light dosimeters. Moreover, the results highlight that both the C10-DNTT and the PDBPyBT layer function as photo exciton generation and charge-trapping layers. Last, we seek to fabricate cost-effective organic multilayer devices through a solution-processing approach, eliminating the need for orthogonal solvents. We observe a crosslinking effect in the thin films caused by thermal annealing without using any crosslinker. Remarkably, this effect is found to be universal for several commercial semiconducting polymers investigated in our study. Following annealing at 200 ºC or higher temperatures, the thin films exhibit enhanced stability against the original solvent. Various analytical techniques are employed to examine the thin films to gain insights into the microstructural changes. Our results suggest that the observed crosslinking effect is predominantly attributed to a physical transformation, whereby the films became more crystalline after annealing at relatively high temperatures. To further explore the feasibility of fabricating multilayer devices, we simulate the construction of multilayer devices by top-gate-bottom-contact (TGBC) devices using the same solvent for the polymer dielectric layer and the semiconducting layer. We also fabricated planar polymer/polymer heterojunction via this method. Encouragingly, this approach demonstrated that thermal annealing could work as a straightforward and promising method for producing cost-effective organic multilayer devices, e.g., fully solution-processed diodes, functional transistors, and solar cells.:Abstract iii Contents vii 1 Introduction 1 1.1 Motivation 1 1.2 Organic semiconductor 2 1.2.1 Atom orbitals and molecular orbitals 2 1.2.2 Energy levels in solid 5 1.2.3 Fermi level 6 1.2.4 Band bending 7 1.2.5 From orbital to states 8 1.2.6 Organic semiconductor materials 9 1.2.7 Nanographene 10 1.2.8 Charge carrier transport in organic semiconductors 11 1.3 Organic field-effect transistors (OFET) 11 1.3.1 OFET architectures 12 1.3.2 OFET operation principle 12 1.3.3 OFET performance parameters 14 1.3.4 OFET memory 17 1.4 Optical electronics 20 1.4.1 Exciton pair generation. 20 1.4.2 Photoelectronic devices 21 1.4.3 Phototransistor devices 22 1.5 Phototransistor memories 23 1.5.1 Working mechanism of phototransistor memories 23 1.5.2 Phototransistor memory architecture 24 1.5.3 State-of-the-art organic phototransistor memory 25 1.6 Objective and outline 27 2 Materials and methods 29 2.1 Materials 29 2.2 Device fabrication 30 2.2.1 Substrate cleaning 30 2.2.2 Solution shearing 30 2.2.3 Thermal vapor deposition 31 2.3 Characterization 31 2.3.1 Thin film characterization 31 2.3.2 Current voltage characteristics 35 2.3.3 Capacitance 36 3 C10-DNTT/NG planar heterojunction phototransistor memories 37 3.1 Introduction 37 3.2 Thin films 39 3.2.1 Film and device fabrication 39 3.2.2 Characterization of thin films 39 3.3 Transfer characteristics under light 41 3.3.1 Writing process 41 3.3.2 Erasing process 48 3.3.3 C10-DNTT-only devices 51 3.4 Summary of working principle 52 3.5 Output characteristics and evaluation of the optical properties 52 3.6 Memory properties of NG-based OPT memory devices 55 3.7 Devices with different NG thicknesses 56 3.7.1 The impact of NG thickness 56 3.7.2 Devices fabricated from 0.05 mg ml-1 NG solution 60 3.8 Conclusion 64 4 C10-DNTT/PDBPyBT heterojunction phototransistor memories 67 4.1 Introduction 67 4.2 Device Architecture 68 4.3 Physical characterization of PDBPyBT and C10-DNTT thin films 69 4.4 Performance of devices with a thick PDBPyBT layer 72 4.4.1 Erasing and programming process 72 4.4.2 Response to different colors of light 78 4.5 Variation of PDBPyBT thickness 80 4.5.1 Transfer characteristics 80 4.5.2 Morphology of C10-DNTT 85 4.5.3 Output characteristics 86 4.5.4 Multi-level programming test 86 4.6 Comparison of the devices 92 4.7 Summary 93 5 Organic multilayer devices fabricated via thermal annealing 95 5.1 Introduction 95 5.2 Film Fabrication 97 5.3 Study on thin films 97 5.3.1 Thickness changes 97 5.3.2 Characterization of the thin films 99 5.3.3 Impact of re-annealing 107 5.3.4 Other semiconducting polymers 108 5.4 Discussion of the working mechanism 110 5.5 Impact of thermal annealing on devices’ performance 111 5.5.1 BGTC devices fabrication 111 5.5.2 TGBC devices fabrication 113 5.6 Planar heterojunction devices via solution processing 116 5.7 Conclusion 117 6 Conclusions and outlook 119 6.1 Conclusions 119 6.2 Outlook 120 Bibliography 123 List of Figures 143 List of Tables 155 List of abbreviations 157 Appendix A 159 Appendix B 165 B1.1 Introduction 165 B1.2 Devices with a 7 nm shear coated Al2O3 dielectric 166 B1.2.1 Normal-sized channel devices 166 B1.2.2 Ultra-wide channel devices 167 B1.3 Devices with a 30 nm ALD Al2O3 dielectric 169 B1.3.1 Normal-sized channel devices 169 B1.3.2 Ultra-wide channel devices 170 B1.4 Ferroelectric organic phototransistor devices 172 B1.4.1 Dielectric layer 172 B1.4.2 Devices with 10 nm HZO 173 B1.4.3 Devices with 30 nm HZO 175 Conclusion 176 Publications 177 Acknowledgment 179

Mon travail de thèse porte sur l’assemblage supramoléculaire et le transport de charge des multi-composants utilisés dans le domaine de l’électronique à base organique. En particulier, l’étude et l’optimisation des transistors organiques à effet de champ (OFETs), des phototransistors, et des inverseurs organiques. Nous avons démontré que la température de recuit des dispositifs OFETs améliore les performances électriques d’un dérivé de fullerène (ICBA). Ces dispositifs dont les surfaces de SiO2 sont fonctionnalisées par OTS ou HMDS ont montrés des mobilités d’électrons de 0.1cm2V-1s-1, qui est la plus élevée par rapport à la littérature. Aussi, nous avons fabriqué des phototransistors à base de mono- et multifibres de PDIF-CN2 qui ont été optimisés par traitements de surfaces du diélectrique (HMDS ou OTS). Les propriétés optoélectroniques de ces dispositifs ont été comparées à ceux des dispositifs à base des couches minces déposés par spin-coating (éduction centrifuge). Nos dispositifs mono-fibres ont montré des valeurs de mobilité plus élevées (supérieure à 2 cm2V-1s-1) par rapport à ceux des multifibres et couches minces. Une telle efficacité de transport d’électrons est le résultat d’une cristallinité très élevée des fibres, qui permet une collecte efficace des excitons photo-générés qui se traduit par la plus haute sensibilité à la lumière (R) et photosensibilité (P) rapportées pour les phototransistors à base de mono-fibre supérieure à 2 × 103 AW-1, et 5 × 103 AW-1. Enfin, un polymère ambipolaire (DPPT-TT) a été utilisé lors de la fabrication de nouveaux dispositifs multifonctionnels par l’addition des molécules diaryléthènes (DAE_tBu et ou DAE_F), dont les propriétés électriques sont contrôlées par la lumière. Cette approche a permis un contrôle optique de gain en tension des inverseurs organiques, ces dispositifs multi-composants sont caractérisés par des gain en tensions très élevées (jusqu’au 504) comparés à ceux reportés dans la littérature (86). Ces travaux réalisés durant cette thèse offrent de nouvelles perspectives dans le domaine de l’optoélectronique et la conception des mémoires optiques. / This thesis is focused on the investigation of supramolecular assemblies and the charge carriers transport across organic single, bi- and three-component materials, used as the active layer in organic field-effect transistors (OFET), phototransistors (OPT) and complementary inverters. We demonstrated that thermal annealing and duration has high impact in OFET performances based on a fullerene derivative called ICBA. The devices electron mobility enhanced upon HMDS and OTS treated SiO2 surface and reached 0.1 cm2V-1s-1, which is the highest reported value in literature. We have provided evidence for the influence of the order at the supramolecular level in the semiconducting material (PDIF-CN2) on the performance of OPTs. We compared solution processed single crystalline PDIF-CN2 fibers and multifiber assemblies with spin-coated thin films, which revealed that the former exhibited good electron mobility up to 2 cm2s-1V-1. The improved fiber crystallinity allows efficient collection of photogenerated excitons, results in the highest reported responsivity R (>5 × 103 AW-1), and photoswitching ratio P (>2 × 103), which are to date the highest reported in literature for PDI-single crystal OPTs. Finally, we have performed for the first time new multifunctional devices combining an ambipolar polymer (DPPT-TT) with inserted diarylethene molecules in its matrix. The fabricated OFET and organic complementary inverters were optically controlled. The resultant inverters gain values are tuned by ultraviolet and visible light irradiation, reaching 504, which is higher than those reported in literature (86). These findings qualify them as promising potential candidates for the construction of high-performance integrated logic circuits and memory chips.