Development of Perovskite-based Solar Cells for Indoor Photovoltaics

Indoor photovoltaics (IPVs) are emerging as a vital technology for powering low-power electronic devices, particularly in the rapidly expanding Internet of Things (IoT) ecosystem. Perovskite solar cells (PSCs) stand at the forefront of IPV research, demonstrating remarkable potential under lowlight conditions due to their exceptional optoelectronic properties and high indoor power conversion efficiencies (iPCEs). This thesis explores two key studies aimed at advancing the performance and stability of PSCs for both indoor and outdoor applications. The first study focuses on enhancing PSC performance and stability using three iodide-based passivation layers including Phenethyl Ammonium Iodide (PEAI), Octyl Ammonium Iodide (OAI), and Guanidinium Iodide (GUI) along with the Lewis base molecule 1,3- bis(diphenylphosphino)propane (DPPP), which, to the best of current knowledge, has not been reported before and is introduced for the first time in n-i-p structured PSCs in this thesis. Scanning electron microscopy (SEM) and X-Ray diffraction (XRD) results revealed that among all samples, the DPPP-passivated sample demonstrated superior morphological and structural stability after aging in ambient environment for a year compared to the other counterparts. Moreover, under 1000 lux light-emitting diode (LED) light illumination, the device incorporating DPPP achieved highest iPCE of 33.14%, close to the highest iPCE of 34.47% obtained by a device incorporating PEAI. Additionally, the device incorporating DPPP exhibited the highest stability under thermal stress (85°C) and 1000 lux indoor light illumination with T80 (time taken for the cell performance to drop to 80% of its initial value) of 753 hrs. The second study delved into the role of dopants in 2,2',7,7'-Tetrakis[N,N-di(4- methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD) hole transport layer (HTL) for PSCs under indoor lighting. Low-temperature planar n-i-p structure devices based on a SnO₂ electron transport layer (ETL) were fabricated, demonstrating adaptability to flexible substrates. While doped Spiro-OMeTAD devices delivered exceptionally higher efficiencies under standard 1-sun illumination compared to their undoped counterparts, a different trend emerged under indoor lighting. Under 1000 lux of white light-emitting diode (WLED) illumination, devices with undoped Spiro-OMeTAD achieved comparable efficiencies (with highest iPCE of 28.37%) with reduced hysteresis compared to doped devices (highest iPCE of 29.36%). Furthermore, under extremely low-light conditions (50 lux), the undoped devices outperformed their doped counterparts, achieving a highest iPCE of 13.65%, compared to the doped devices maximum iPCE of approximately 4%.xvii Additionally, despite the growing emphasis on environmentally friendly fabrication processes for PSCs, triple-cation perovskite (PVK) absorbers synthesized with the eco-friendly solvent anisole as antisolvent, remain unexplored in IPVs. This thesis also bridges this gap, representing a significant step toward greener PVK-based IPV technologies. Overall, the thesis results underscore the potential of innovative passivation strategies to optimize PSCs performance and stability under low-light conditions and highlights the significance of ETL materials and the potential of undoped HTLs for achieving efficient and stable PSCs under challenging indoor lighting environments.