Study of electron-transport-layer-free and hole-transport-layer-free inverted perovskite solar cells

The selective contacts in perovskite solar cells play a major role in solar cell (SC) performance and optimization. Herein, the inverted architecture is focused on, where systematically the electron transport layer (ETL) and the hole transport layer (HTL) from the SC structure are eliminated. Three main architectures of the SCs are studied: a fully inverted structure, an ETL-free structure, and a HTL-free structure. Cathodoluminescence and photoluminescence are measured on various architectures, revealing the electron and hole injection efficiency from the perovskite to selective contacts. Moreover, surface voltage spectroscopy shows the type and the band-edge transition of these layers. Finally, the photovoltaic (PV) performance of different SCs shows that eliminating the HTL is most critical for PV performance, compared with ETL-free and fully inverted SC configurations. Current-voltage hysteresis curves prove that efficient selective contacts are essential to eliminate this phenomenon. Measuring the ideality factor shows that the dominant mechanism in ETL-free SCs is surface recombination, whereas in the other cases, it is Shockley-Reed-Hall recombination. This work provides knowledge about the functionality of methylammonium lead iodide as an electron conductor and as a hole conductor.