Effect of ZnO and PEDOT:PSS charge selective layers on photovoltage of cuprous oxide (Cu2O) heterojunction solar cells

Electrochemical deposition (ECD) of Cu2O provides a scalable and low temperature pathway to solar cells with a theoretical high energy conversion efficiency of 23%, based on the 2.0-2.2 eV band gap of Cu2O. However, existing ECD-Cu2O devices are plagued by poor crystallinity and low selectivity of the electron and hole transport layers. Here we use Vibrating Kelvin Probe Surface Photovoltage Spectroscopy (VKP-SPV) to probe the charge transfer selectivity in FTO/ZnO/Cu2O/PEDOT:PSS/Ni heterojunction solar cells. Selective electron extraction is achieved at the ZnO back contact to Cu2O, as confirmed by a negative surface photovoltage signal. While the uncoated Cu2O surface is electron-selective due to the formation of a hole depletion layer, spin coating of a PEDOT:PSS film turns it into a hole-selective interface. After adding nickel metal ink top electrodes, functional 1.0 cm(2) solar cells with power conversion efficiency (PCE) of up to 0.07%, 195 mV open-circuit voltage, and 1.28 mA cm(-2) short-circuit photocurrent are achieved. The photovoltaic performance is higher for aluminum doped zinc oxide (AZO) substrates than for fluorine doped tin oxide (FTO) due to the presence of a n-/p-junction that further increases the electron selectivity of the AZO/ZnO/Cu2O contacts. Overall, this work demonstrates the first application of PEDOT:PSS as a hole transport layer (HTL) for Cu2O and the use of VKP-SPV to measure the photovoltage contributions of the Cu2O interfaces. The ability to fabricate Cu2O solar cells at near room temperature without the use of vacuum methods or rare elements is an important step towards a scalable Cu2O PV technology.