Interface engineering of high performance organic and perovskite solar cells

Both organic and perovskite solar cells (OSCs and PSCs, respectively) have shown remarkable progress in recent years reaching power conversion efficiencies (PCEs) of 17.6% and 25.2% for a single cell, respectively. These results were achieved by simultaneous advancements in organic and perovskite materials design and synthesis, as well as device and interfacial engineering. As these emerging photovoltaic technologies move closer to commercialization, further improvements in efficiencies and stability of the solar cells are needed. Interfaces in these thin-film solar cells have proven to be of tremendous importance for both device performance and degradation. This work is focused on studying recombination losses at the charge extracting layers in OSCs and PSCs and finding simple solution-processable ways of improving interfacial contacts. In the first part, we propose a simple way to improve the electron extracting properties of Phen-NaDPO, a small organic molecule widely used in OSCs, by mixing it with Sn(SCN)2. We show that this approach benefits morphology and charge transport, thus reducing recombination losses and improving overall performance of various bulk heterojunction OSCs and PSCs. In the second part, we describe the development of a multilayered system of electron transporting interlayers (ETLs) to improve the PCE and operational stability of PSCs. We sequentially deposit PC60BM, Al-doped ZnO (AZO), and small organic molecule triphenyl-phosphine oxide (TPPO), and study how the ETL properties and device performance change with each layer. We find that the trap-assisted recombination and energy level alignment in PSCs improve due to specific chemical interactions between PC60BM, AZO, and TPPO. The third part is divided into two and is focused on CuSCN, a wide bandgap inorganic molecular hole transporting material, and its application in OSCs. In the first half, we study the recombination and photogeneration processes in PC70BM-only OSCs. We demonstrate that CuSCN plays a crucial role in excitons dissociation and efficient charge transfer at the CuSCN/PC70BM interface. In the second half, we optimize CuSCN layers’ structural and electronic characteristics using a simple solvent engineering approach. We study how processing conditions affect the morphological, chemical, optical, and electronic properties of CuSCN and how they impact the OSCs’ performance.