Fill Factor Assessment in Hole Selective Layer Free Carbon Electrode-Based Perovskite Solar Cells with 15.5% Certified Power Conversion Efficiency

Carbon-electrode-based perovskite solar cells (C-PSCs) are promising candidates for commercialization due to their high stability. However, the absence of a hole selective layer (HSL) often limits their performance, yielding low fill factors (FFs). Herein, a certified FF of 78.8% obtained through HSL-free C-PSCs is focused. This is found to approach the highest values reported for metal-electrode-based PSCs employing highly selective HSLs. The loss mechanisms affecting the FF in fully printed HSL-free C-PSCs are thus investigated. Methods commonly used to analyze and quantify the impact of recombination and transport losses on the FF of established photovoltage devices are assessed, and their applicability in C-PSCs is examined. In the improved devices, non-radiative recombination contributes to only 3%abs loss with respect to the FF in the radiative limit, which is attributed to an optimal diode ideality factor approaching 1.0. Moreover, contributions of shunt resistive losses are determined to be negligible. Interfacial series resistance losses at the perovskite/carbon interface are identified as the main loss channel, highlighting the importance of the quality of the contact between the perovskite and the back-contact electrode.