Asian Research Thesis Index

Abstract

Silicon is still the dominant photovoltaic technology with over 90% share in the solar cell  market. Prices of silicon solar cells have drastically reduced in the past few years which has led to its  widespread adoption, but manufacturing of these cells requires huge capital and running cost and the  processes involved are extremely time and energy intensive.For solar cells to become ubiquitous  their cost needs to be significantly lowered. This can be done through new approaches which involve  cheap materials and easy processing. Perovskite and dye sensitized solar cells have emerged as cost effective alternatives to the silicon solar cells due to their simple and easy processing and inexpensive  constituents. Although perovskite solar cells have demonstrated a lab scale power conversion  efficiency of over 22% but their ambient air synthesis and long-term stability against moisture and  water remains a challenge to their commercial exploitation. Different approaches including a water  resistive top coating on perovskite cells, substituting iodide with chloride ion and methyl group with  formamidinium cation, constructing two-dimensional layered morphologies and morphology  engineering using co-solvents and additives have been explored to address these issues.  Among these approaches, additive engineering due to its ease of incorporation, simplicity and  unprecedented control over the nature and architecture of substituents offers huge advantage over  all the rest.This thesis presents results of the ambient-air synthesis and stability studies of perovskite  solar cells prepared using additives with hydrophobic and hydrophilic substituents. To realize  perovskite solar cells two-step approach was employed. Ethanolamine (EA), dibutylamine (DBA) and  dibutylethanol amine (DBEA) were used as complexing agents to modify the nucleation and  crystallization behavior of lead iodide during film formation. All three additives significantly enhanced  solubility of lead iodide in dimethylformamide (DMF). Perovskite films prepared using EA, DBA and  DBEA showed much improved surface coverages, larger and uniform grain sizes and much enhanced  uniformities compared to pristine film, which exhibited gross phase separation. Power conversion  efficiencies (PCE) of over 3%, 5% and 10.8% were obtained for EA, DBA and DBEA incorporated  perovskites whereas pristine devices exhibited PEC values of under 1%.Photoluminescence (PL)  spectroscopy confirms IV results that charge recombination is drastically reduced by the addition of  these additives and the lowest recombination was observed for DBEA. Similar trend was observed for  air-stability tests where DBEAincorporated devices showed highest stability (over 750 h) followed by  DBA (over 500 h) and then EA (less than 200 h). Under same environmental conditions, pristine devices  were found to be completely degraded within 150 h. Second part of this thesis reports on the efficiency enhancement of dye sensitized solar cells by  directly depositing gold (Au) nanoparticles on the mesoporous titania scaffold before dye  xii   sensitization. Cells based on these photoanodes showed 9.48% efficiency compared to 6.1% for the  reference cell, exhibiting an overall enhancement of 55% using only 0.11 wt% of Au, which is the  lowest reported Au concentration for DSSCs in the literature to-date. We also report on the use of  biomass-derived nitrogen-doped carbon aerogel as an effective alternative to conventional platinum based counter electrodes for dye sensitized solar cells. The nitrogen-doped carbon aerogel electrode,  deposited from oleylamine mixture, was annealed at different temperatures and its impact on  photovoltaic performance of these cells is investigated. I-V measurements confirm that the annealing  temperature substantially enhances photovoltaic parameters of these devices. The power conversion  efficiency of the solar cells from optimized nitrogen-doped carbon aerogel exhibited comparable  efficiency to that of a cell fabricated using platinum-based counter electrode.

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