Morphology Control And Interface Engineering Of Organic And Perovskite Opto-electronics

Organic and perovskite opto-electronics have attracted tremendous attentions from academia and industry due to their unique advantages such as highly tunable properties,low cost,light weight,flexibility,and compatibility of solution-processing.Morphology of active layer plays a critical role in determining the exciton dissociation and charge carrier transport efficiency,and thus,the device performance of organic and perovskite opto-electronics.Therefore,achieving active layer with favorable morphology and quality is of great importance.In this thesis,we focus on the optimization of active layer and its interface of organic and perovskite optoelectronics,try to develop efficient and stable organic and perovskite solar cells and high performance organic near-infrared photodetectors.In the chapter 2,liquid-phase-exfoliated black phosphorus nanoflakes were applied to organic solar cells as morphology modifier.The active layer blends incorporated with black phosphorus nanoflakes exhibit more ordered molecular stacking and promoted domain purity,contributing to more efficient charge transport and collection within the device.As a result,power conversion efficiency（PCE）enhancement was observed in organic solar cells employing several active layer systems.Besides,the embedded black phosphorus nanoflakes help to improve the morphological stability of the devices probably by retarding the phase mixing in the bulk hetero-junction during thermal aging.In the chapter 3,we employed liquid-phase-exfoliated black phosphorus quantum dots as additives in the perovskite precursor solution to tailor the growth of methylammonium lead iodide films.We found that black phosphorus quantum dots serve as heterogeneous nucleation centers during the solvent-processing crystallization of perovskite,leading to the high-quality perovskite film with higher crystallinity and less defects.As a result,perovskite solar cells with black phosphorus quantum dots show significantly improved PCE of 20.0%（with a reference PCE of 17.7%）as well as better thermal stability.In the chapter 4,influence of interfacial layer on the thermal stability of perovskite was thoroughly investigated.The overall degradation of perovskite was distinguished into chemical decomposition due to chemical active sites,and mechanical fracture due to thermal stress resulted from mismatched thermal expansion coefficients.As for the chemical decomposition,there are two parallel paths taking place in active layer bulk and in active layer/interfacial layer interface,respectively.Combining experiment and simulation,we demonstrated the qualities desired for a good interfacial layer,including capability of thick layer（>20 nm）utilization,low modulus（few GPa or less）,low chemical activity.Accordingly,a bi-layer polymer interfacial layer was designed and prepared,offering a high PCE of 18.8%and promising improved thermal stability,remaining 80%of its initial PCE after aging at 100℃ for 600 h.In the chapter 5,origin of dark current in organic photodetectors was analyzed.We found that when the direct charge injection from the electrode at reverse bias is effectively blocked,there remains a component of traps-induced generation current in the device.By "diluting" hole blocking layer C60 in the LiF insulator matrix,traps effect in active layer/blocking layer interface can be significantly surpressed.As a result,we have demonstrated organic near-infrared photodiodes with a dark current density of 0.2 nA cm^-2 at-2 V and specific detectivity of over 10¹³ Jones at wavelengths up to 940 nm,which is in the same level as the commercial siliconbased photodiodes.