Enhancing the efficiency and stability of perovskite solar cells

Abstract

Organic-inorganic hybrid perovskite materials have demonstrated their potential in photovoltaic application in recent years. Apart from the effort on further improving the power conversion efficiencies (PCEs) of perovskite solar cells (PSCs), the stability of PSCs remains a key concern for technological application. In this thesis, approaches of improving PCEs of PSCs, and enhancing the stability under environmental stresses, are investigated. The first results chapter investigates the improved oxygen induced photodegradation in inverted structure PSCs in comparison to conventional structure PSCs. The enhanced stability is attributed to PCBM passivation and slow oxygen diffusion kinetics in the inverted structure PSC. The second results chapter demonstrates that the addition of aminovaleric acid (AVA) in methylammonium lead iodide (MAPbI3) light absorber can effectively enhance the stability of unencapsulated PSC against oxygen induced photodegradation. The enhanced stability is also observed in glass/perovskite thin film, indicating the enhanced stability is not dependent on other interlayers but perovskite material itself. AVA is found to be located at the surface of perovskite lattice, binding to the surface defects, resulting in improved stability. The third results chapter shows that the use of bulky cation 1-naphthylmethylamine (NMA) as an additive in MAPbI3 and wider band gap perovskite (MAPbI1-xBrx)3 light absorbers can minimize the Voc losses in inverted structure PSC. The enhanced Voc results from NMA terminated at grain surface, passivating the traps and suppressing the non-radiative recombination. The forth results chapter investigates the power conversion efficiencies (PCEs) and stability of inverted structure PSCs with different sizes of amino acids additives in MAPbI3 light absorber, showing that the addition of smallest amino acid, glycine, can not only enhance Voc but also stability of inverted structure PSC. The last results chapter shows that employing bilayer Cu/Ag electrode can improve the operational stability of unencapsulated inverted structure PSC.