Small molecules for applications in solar cells

Abstract

This thesis studies the application of small molecules such as benzoic acids and perylene diimides as interlayers and charge transporting layers in perovskite solar cells. As promising new generation photovoltaics, perovskite solar cells have drawn much attention from scientists around the world due to the high power conversion efficiencies and relatively low energy consumption required during the fabrication process. However, many problems still need to be addressed such as improving stability, reducing hysteresis and removing the expensive charge transporting layers (e.g. spiro-OMeTAD is £850/5g). All of these problems are slowing commercialization of perovskite cells. Work in this thesis starts with the optimization of the baseline perovskite solar cells, including optimizing the methods of thin film semiconductor preparation, the device architecture and device pattern. By the end of the project average PCE that were consistently above 11% (prepared either in a dry box or in ambient environment) with a narrow distribution were achieved. Further studies into hysteresis and device characterization were also carried out in this part. Interface engineering was investigated by using perylene diimides (PDIH and PDIV) and benzoic acids (4-aminobenzoic acid, 4-(aminomethyl benzoic acid and 4-(methylamino) benzoic acid) as interlayers to modify the compact TiO2 layer. Methods to prepare the thin interlayers were optimized and the impacts of the interlayers on the film crystallization, device PCE, stability and hysteresis were also studied. Interlayers were found to significantly change the morphology of the perovskite layer (all molecules), enhance the short circuit current (benzoic acids), and improve the PCE (PDIH) and stability (PDIH). Finally PDIH was studied as the electron transporting layer to replace the TiO2 film as it can be processed at low temperature (compared with TiO2). The parameters to fabricate the PDIH layer were optimized and devices with a PCE of 5.7% on average and enhanced stability were achieved.

Date of Award	7 Nov 2017
Original language	English
Awarding Institution	University of Bath
Supervisor	Petra Cameron (Supervisor) & Laurie Peter (Supervisor)