Low power electronics are an ideal application for organic photovoltaics (OPV) where a low‐cost OPV device can be integrated directly with a battery to provide a constant power source. We demonstrate ultra‐high voltage small molecule multijunction devices with open circuit voltage (VOC) values of up to 7V. Optical modelling is employed to aid the optimisation of the complex multi‐layer stacks and ensure current balancing is achieved between sub‐cells, and optimised multijunction devices show power conversion efficiencies of up to 3.4% which is a modest increase over the single junction devices. Sub‐cell donor/acceptor pairs of boron subphthalocyanine chloride (SubPc)/fullerene (C60) and SubPc/Cl6‐SubPc were selected both for their high VOC in order to minimise the required number of junctions, but also for their absorption overlap to reduce the spectral dependence of the device performance. As a result, the devices are shown to directly charge a micro‐energy cell type battery under both low illumination intensity white light and monochromatic illumination.

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Spray deposition is currently attracting significant attention as a low cost method for organic photovoltaic (OPV) device fabrication. We report indium tin oxide (ITO)-free small moleule OPV devices comparing spin coated and spray deposited highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the transparent conducting electrode (TCE). Conductive atomic force microscopy studies indicate that despite an increase in surface roughness, spray deposited PEDOT:PSS TCEs display a similar distribution in the surface composition of PEDOT and PSS and provide comparable device performance to spin coated PEDOT:PSS TCEs. Therefore, the TCEs fabricated by spray deposition show potential as an inexpensive solution processable alternative to the conventionally used ITO TCE for OPV devices.