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Novel Atmospheric Growth Technique to Improve Both Light Absorption and Charge Collection in ZnO/Cu2O Thin Film Solar Cells



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.