Electrodeposited Cu 2 O-ZnO heterojunctions are promising low-cost solar cells. While nanostructured architectures improve charge collection in these devices, low open-circuit voltages result. Bilayer and nanowire Cu 2 O-ZnO heterojunction architectures are systematically studied as a function of the Cu 2 O layer thickness, ZnO nanowire length, and nanowire seed layer. It is shown that a thick depletion layer exists in the Cu 2 O layer of bilayer devices, owing to the low carrier density of electrodeposited Cu 2 O, such that the predominant charge transport mechanisms in the Cu 2 O and ZnO are drift and diffusion, respectively. This suggests that the low open-circuit voltage of the nanowire cells is due to an incompatibility between the nanostructure spacing required for good charge collection ( < 1 μ m) and the heterojunction thickness necessary to form the full built-in potential that inhibits recombination ( > 2 μ m). The work shows the way to improve low-cost Cu 2 O cells: increasing the carrier concentration or mobility in Cu 2 O synthesized at low temperatures.

A novel buffering method is presented to improve the stability of zinc oxide processed in aqueous solutions. By buffering the aqueous solution with a suitable quantity of sacrificial zinc species, the dissolution of functional zinc oxide structures and the formation of unwanted impurities can be prevented. The method is demonstrated for ZnO films and nanowires processed in aqueous solutions used for the selective etching of mesoporous anodic alumina templates and the electrochemical deposition of Cu2O. In both cases, improved ZnO stability is observed with the buffering method. ZnO‐Cu2O heterojunction solar cells (bilayer and nanowire cells) synthesized using both traditional and buffered deposition methods are characterized by impedance spectroscopy and solar simulation measurements. Buffering the Cu2O deposition solution is found to reduce unwanted recombination at the heterojunction and improve the photovoltaic performance.

Phase pure, dense Cu2O thin films were grown on glass and polymer substrates at 225°C by rapid atmospheric atomic layer deposition (AALD). Carrier mobilities of 5 cm2V−1s−1 and carrier concentrations of ∼1016 cm−3 were achieved in films of thickness 50 - 120 nm, over a >10 cm2 area. Growth rates were ∼1 nm·min−1 which is two orders of magnitude faster than conventional ALD.. The high mobilities achieved using the atmospheric, low temperature method represent a significant advance for flextronics and flexible solar cells which require growth on plastic substrates

In low temperature grown ZnO/Cu2O solar cells, there is a discrepancy between collection length and depletion width in the Cu2O which makes the simultaneous achievement of efficient charge collection and high open‐circuit voltage problematic. This is addressed in this study by fabricating ZnO/Cu2O/Cu2O+ back surface field devices using an atmospheric atomic layer deposition (AALD) printing method to grow a sub‐200‐nm Cu2O+ film on top of electrodeposited ZnO and Cu2O layers. The AALD Cu2O+ has a carrier concentration around 2 orders of magnitude higher than the electrodeposited Cu2O, allowing the electrodeposited Cu2O layer thickness in a back surface field cell to be reduced from 3 μm to the approximate charge collection length, 1 μm, while still allowing a high potential to be built into the cell. The dense conformal nature of the AALD layer also blocks shunt pathways allowing the voltage enhancement to be maintained. The thinner cell design reduces recombination losses and increases charge collection from both incident light and light reflected off the back electrode. Using this design, a short circuit current density of 6.32 mA cm−2 is achieved–the highest reported JSC for an atmospherically deposited ZnO/Cu2O device to date.

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