a Photovoltaic metrics of devices without Cs doping (control), with homogeneous Cs doping, after treatment with DB21C7–CsI (target) and after just crown ether (DB21C7) treatment. b J–V curves of the champion control and target PSCs. The inset shows the maximum power point tracking data. An anti-reflection coating was used for the champion devices. c Photoluminescence spectral photon flux Φ measured on full devices. d Breakdown of losses derived from the J–V curves in b; radiative JSC and VOC losses are shown in green and grey, respectively; non-radiative VOC and FF losses in black and red; transport losses affecting FF in blue.