Carrier gradients and the role of charge selective contacts in lateral heterojunction all back contact perovskite solar cells

Abstract

Realizing photovoltaic devices that achieve the full potential of the metal halide perovskite material will require improved insight regarding the role of selective contacts and how key interfaces operate when mobile defects are present. However, measuring interface properties in typical device stacks where the perovskite layer is thin and sandwiched between two contacts has been a challenge. Here, we fabricate p-i-n and p-n lateral heterojunctions with nickel oxide/titanium oxide all back contacts, permitting us to employ a comprehensive analysis approach, including ultraviolet and X-ray photoemission spectroscopy (UPS/XPS), angle-resolved X-ray absorption spectroscopy (XAS), Kelvin probe force microscopy (KPFM), surface photovoltage (SPV), hyperspectral imaging (HSI), and time-resolved fluorescence lifetime imaging microscopy (TR-FLIM) to discern the role of selective contacts. Specifically, we tune the selectivity of the contacts, changing the gradient in the carrier concentration across the surface of the active layer, which is connected to carrier extraction at the buried interface, and thus the device functionality. • Charge selective contacts shift the Fermi level in metal halide perovskites (MHPs) • Effect is readily observable because of low defect and doping concentrations in the MHP • Contact selectivity determines carrier extraction across MHP/contact interfaces • Tailoring charge selective contacts to design MHP-based lateral heterojunction devices Metal halide perovskites (MHPs) define an emerging field of novel optoelectronics. For MHP-based applications, such as interdigitated back contact solar cells, the right choice of charge selective contacts remains the principal challenge to overcome; however, relatively few design rules exist because of the unusual defect properties of MHPs. Here, Dunfield et al. employ a range of techniques to discern the role of selective contacts.