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Here, we report an experimental demonstration of perovskite solar cells dominated by bimolecular recombination and critically analyse their performance against radiative limits. To this end, we first establish a set of quantitative benchmark characteristics expected from solar cells limited by bimolecular recombination. Transient as well as steady state intensity dependent measurements indicate that our solar cells indeed operate at such limits with interface passivation comparable to the champion c-Si technology. Further, we identify novel characterization schemes which enable consistent back extraction of recombination parameters from transient optoelectrical and electroluminescence measurements. Remarkably, these parameters predict important features of dark current density vs. voltage characteristics (J-V) and Suns-V_OC measurements, thus validating the estimates and the methodology. Uniquely, this work provides a consistent and coherent interpretation of diverse experimental trends ranging from dark J-V, Suns-V_OC, steady state and transient intensity dependent measurements to electroluminescence quantum yield. As such, insights shared in this manuscript could have significant implications towards fundamental electronic processes in perovskite solar cells and further efficiency optimization towards Shockley-Queisser limits., Comment: Accepted in ACS Energy Letters

[4-(3,6-dimethyl-9H-carbazole-9-yl)butyl]phosphonic acid (Me-4PACz) self-assembled monolayer (SAM) has been employed in perovskite single junction and tandem devices demonstrating high efficiencies. However, a uniform perovskite layer does not form due to the hydrophobicity of Me-4PACz. Here, we tackle this challenge by adding a conjugated polyelectrolyte poly(9,9-bis(3'-(N,N-dimethyl)-N-ethylammonium-propyl-2,7-fluorene)-alt-2,7-(9,9dioctylfluorene)dibromide (PFN-Br) to the Me-4PACz in a specific ratio, defines as Pz:PFN. With this mixing engineering strategy of Pz:PFN, the PFN-Br interacts with the A-site cation and is confirmed via solution-state nuclear magnetic resonance studies. The narrow full width at half maximum (FWHM) of diffraction peaks of perovskite film revealed improved crystallization on the optimal mixing ratio of Pz:PFN. Interestingly, the mixing of PFN-Br additionally tunes the work function of the Me-4PACz as revealed by the Kelvin probe force microscopy and built-in-voltage estimation in solar cells. Devices employing optimized Pz:PFN mixing ratio deliver open-circuit voltage (Voc)of 1.16 V and efficiency >20% for perovskites with a bandgap of 1.6 eV with high reproducibility and concomitant stability. Considering significant research on Me-4PACz SAM, our work highlights the importance of obtaining a uniform perovskite layer with improved yield and performance.