Stability enhancement in solution-processed perovskite solar cells

Department of ChemistryThe high cost and complexity of fabrication in silicon based photovoltaic (PV) provoked considerable research interest for alternative solution-processed photovoltaic solar cells. Organic-inorganic perovskite solar cells gained attention as they high defect tolerance, high absorption coefficient, low defect density, long diffusion lengths, and low low-exciton binding energy, also they achieved comparable higher efficiency than single junction Si-solar cells. However, compared to the established PV technologies, organic-inorganic perovskite solar cells lacks in terms of stability and degrades easily under the influence of light, humidity, and moisture. All-inorganic solar cells offer better thermal and photo-stability compared to their counterpart perovskite solar cells because they have non-volatile compounds in their 3D lattice structure. The structural and air stability of CsPbI3 is hindering the researchers to explore the full potential but addition of excess HI or zwitterions assisted methods solved the structural issue to some extent. This thesis aims to solve stability issues in perovskite materials and find their application in highly efficient optoelectronic devices. In the 1st chapter, we introduced in detail, the basic properties of perovskite material, the essential parameters of solar cells, the device architecture, and the mechanism related to perovskite degradation. Also, we discussed the previous techniques to improve the stability in different structures of perovskite solar cells. The 2nd chapter of this thesis aims to stabilize ??-CsPbI3 using barium doping, and its application in optoelectronic devices. In this part, we briefly introduced the general background, metastable behavior. Also our approach for the surface passivated, Ba-doped ??-CsPbI3 exhibit thermal stablity upon annealing as well as highly photo-stable over a year, and it also exhibits ~1.72 eV band gap suitable for optoelectronic applications. All inorganic solar cells based on the Ba-doped ??-CsPbI3 retain 98% of its initial PCE values even after 700 hours, also the red light-emitting diodes (LED) exhibit the light emission at 700 nm with bandwidth 39 nm. In the 3rd chapter, we unfolded the effect of metal doping on the properties of CsPbI3 perovskite by using theory and experimental evidences. The heterovalent metals (i.e. Bi3+, Sb3+) and divalent cations (i.e., Ba2+, Sr2+, and Sn2+) were doped to stabilize the ??-CsPbI3 by replacing the Pb2+ cations. We challenged the earlier assumptions of stabilizing ??-CsPbI3 by heterovalent doping and we demonstrated that the divalent cations stabilize ??-CsPbI3 films, making thermally stable at high temperatures, whereas heterovalent metal-doping stabilizes ??-CsPbI3 films, making metastable. Also, we propose that Sr doping is more favorable for device fabrication because of its better charge dissociation and transport kinetics compared to Ba doped and ??-CsPbI3 perovskite films. In the 4th chapter, we discussed the newly synthesize sulfonated octylammonium materials for passivating the perovskite crystal grain interface to stop ion migration. We incorporate three different octyl-ammonium sulfate compounds, Octylamine functionalized with sulfanilic acid (OAS), p-toluene sulfonic acid (OAT), and camphor sulfonic acid (OAC). We demonstrate that, passivating the grains interface reduces the hysteresis, improves charge recombination and the stability, and also achieved the power conversion efficiency of 18.56% for the control device to 18.26%, 22.09%, and 21.5% for OAS, OAT, and OAC, respectively.clos