Research Projects

Perovskites, especially all-inorganic and 3D perovskites (e.g. CsPbX3, where B-site cation is Pb and X = halide), are a class of materials which can be considered as the potential candidates for fundamental deep-tech optoelectronic applications, starting from LEDs, solar cells to photo-detectors and photo-transistors due to their narrow, colour pure and very bright photoluminescence (PL) emission, exotic photo-physics and excited state charge carrier dynamics. However, these 3D perovskites suffer from serious stability issue, and ion-migration problem in mixed halide perovskites and these perovskites contain toxic metal Pb, which raises serious sustainability concerns which hinder the sustainable application potential. In order to circumvent these problems, in very recent days, researchers have explored some 0D perovskites where, toxic Pb has been replaced with non-toxic metal like Sn, Zr, Cu, and Zn. These toxic metal free 0D perovskites (TMFZDPs) can compete with CsPbX3 3D perovskites in the following cases : i. 3D perovskites e.g., CsPbX3 suffer from instability, TMFZDPs are stable for several months. ii. Isolated nature of TMFZDPs can suppress the halide ion migration, unlike 3D perovskites. iii. TMFZDPs have high exciton binding energy (~100 meV to as high as ~770 meV), tunable wide band gap, high absorption coefficient, moderate to high PL and high charge transport properties. iv. All these properties in addition to high sensitivity, low dose rate, fast response time etc. along with much low toxicity of B-site cation in comparison to Pb, makes these TMFZDPs comparatively much more suitable for sustainable and highly stable photodetectors and other optoelectronic devices such as LEDs, transistors. As a TMFZDPs, the choices can be Cs2SnX6, Cs2ZrX6, Cs3Cu2X5, Cs2ZnX4 etc., where X = Cl or Br or I This proposed project envisages yielding the following very important goals as well as to provide hitherto unknown structural and dynamical information in TMFZDPs : 1. By performing several synthetic modifications like ligand or doping metal as well as their percentage or temperature variation, different TMFZDPs will be synthesized. 2. TMFZDPs will be characterized structurally as well as elementally through TEM, HRTEM, EDAX, XPS, PXRD, ICP-MS, Raman, EPR analyses etc. 3. From cryogenic (4 K) to high (500 K) temperature PL measurements, information regarding the presence of new PL emission band, mapping of excited state energetics extent of electron-phonon coupling, etc. will be known. 4. From ultrafast to fast to slow excited state dynamics, several time constants for hot electron trapping dynamics, hot electron cooling dynamics or hot hole trapping dynamics will be known. 5. By performing the TRES-TRANES analyses from the ultrafast to slow time regime, detailed excited state energetics, possible presence of intermediate and multiple excited states in between initially excited state and the state from which PL emission occurs, will be known. 6. By performing single particle level charge carrier dynamics or blinking dynamics in TMFZDPs, it will be possible to know the electron and hole trapping and detrapping dynamics and their amplitude variations. 7. From the above investigation, it will be possible to know the rationale behind very large Stokes shifted (~150 – 260 nm) PL emission and the large FWHM of PL emission (~73 – 180 nm or ~300 – 600 meV) in TMFZDPs. 8. Once all these are done, then serious efforts will be made to prepare TMFZDPs with outstanding optical properties (near-unity PLQY, narrow FWHM of PL emission (~40 nm or~100 meV), and stability etc. 9. Finally serious efforts will be made towards achieving sustainable applications of these TMFZDPs towards highly stable and high-performance photo-detectors, photo-transistors etc.