Despite record‐breaking devices, interfaces in perovskite solar cells are still poorly understood, inhibiting further progress. Their mixed ionic‐electronic nature results in compositional variations at the interfaces, depending on the history of externally applied biases. This makes it difficult to measure the band energy alignment of charge extraction layers accurately. As a result, the field often resorts to a trial‐and‐error process to optimize these interfaces. Current approaches are typically carried out in a vacuum and on incomplete cells, hence values may not reflect those found in working devices. To address this, a pulsed measurement technique characterizing the electrostatic potential energy drop across the perovskite layer in a functioning device is developed. This method reconstructs the current‐voltage (JV) curve for a range of stabilization biases, holding the ion distribution “static” during subsequent rapid voltage pulses. Two different regimes are observed: at low biases, the reconstructed JV curve is “s‐shaped”, whereas, at high biases, typical diode‐shaped curves are returned. Using drift‐diffusion simulations, it is demonstrated that the intersection of the two regimes reflects the band offsets at the interfaces. This approach effectively allows measurements of interfacial energy level alignment in a complete device under illumination and without the need for expensive vacuum equipment.

(R,R)‐ and (S,S)‐(2,9‐2H2)‐n‐Decane were prepared regio‐ and stereospecifically in 25–26 % yield over five steps from commercially available enantiopure (R)‐ and (S)‐propylene oxide, respectively. The synthetic procedure involved nucleophilic displacement of (R)‐ and (S)‐4‐toluenesulfonic acid 1‐methyl‐4‐pentenyl ester with LiAlD4 to furnish the respective (5‐2H)‐1‐hexenes. Subsequent olefin metathesis and reduction of the double bond furnished the title compounds. The optical purity of (R,R)‐ and (S,S)‐(2,9‐2H2)‐n‐decane could not be determined by chromatography or polarimetry. Therefore, (R,R)‐ and (R,S)‐(5‐2H)‐3‐hydroxy‐2‐hexanone were prepared from their respective hexenes by Wacker oxidation, followed by enantioselective α‐hydroxylation. The enantiopurity could then be determined by NMR spectroscopy because the stereospecifically deuterated hydroxyketones showed separated signals for the subterminal carbon atom (C‐5) in the 13C NMR spectrum.