Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO.

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O substrates outside vacuum at low temperature. The performance of photovoltaic devices featuring atmospherically fabricated ZnO/Cu2O heterojunction was dependent on the conditions of AP-SALD film deposition, namely, the substrate temperature and deposition time, as well as on the Cu2O substrate exposure to oxidizing agents prior to and during the ZnO deposition. Superficial Cu2O to CuO oxidation was identified as a limiting factor to heterojunction quality due to recombination at the ZnO/Cu2O interface. Optimization of AP-SALD conditions as well as keeping Cu2O away from air and moisture in order to minimize Cu2O surface oxidation led to improved device performance. A three-fold increase in the open-circuit voltage (up to 0.65 V) and a two-fold increase in the short-circuit current density produced solar cells with a record 2.2% power conversion efficiency (PCE). This PCE is the highest reported for a Zn1-xMgxO/Cu2O heterojunction formed outside vacuum, which highlights atmospheric pressure spatial ALD as a promising technique for inexpensive and scalable fabrication of Cu2O-based photovoltaics.The authors acknowledge the support of the Cambridge Overseas and Commonwealth Trust, the Rutherford Foundation of New Zealand, Girton College Cambridge. This work has been funded by ERC Advanced Investigator Grant, Novox, ERC-2009-adG247276 and by the EPSRC (under RGS3717)

Maintaining surface-phase purity is key to efficient open air fabricated cuprous oxide solar cells

This is the final published version. It first appeared at http://scitation.aip.org/content/aip/journal/aplmater/3/2/10.1063/1.4913442.Electrochemically deposited Cu 2O solar cells are receiving growing attention owing to a recent doubling in efficiency. This was enabled by the controlled chemical environment used in depositing doped ZnO layers by atomic layer deposition, which is not well suited to large-scale industrial production. While open air fabrication with atmospheric pressure spatial atomic layer deposition overcomes this limitation, we find that this approach is limited by an inability to remove the detrimental CuO layer that forms on the Cu 2O surface. Herein, we propose strategies for achieving efficiencies in atmospherically processed cells that are equivalent to the high values achieved in vacuum processed cells.The authors acknowledge funding from the Cambridge Commonwealth, European and International Trusts (R.L.Z.H. and Y.I.), Rutherford Foundation of New Zealand (R.L.Z.H.), an NSF Graduate Research Fellowship (R.E.B.), EPSRC of the UK (S.H.), University of Cambridge EPSRC Centre for Doctoral Training in Nanoscience (S.H.), Girton College Cambridge (K.P.M.), an NSF CAREER Award ECCS-1150878 (T.B.), the National Research Foundation Singapore through the Singapore Massachusetts Institute of Technology Alliance for Research and Technology’s Low Energy Electronics Systems research program (T.B.), and an ERC Advanced Investigator Grant, Novox, ERC-2009-adG247276 (J.L.D.)

Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O substrates outside vacuum at low temperature. The performance of photovoltaic devices featuring atmospherically fabricated ZnO/Cu2O heterojunction was dependent on the conditions of AP-SALD film deposition, namely, the substrate temperature and deposition time, as well as on the Cu2O substrate exposure to oxidizing agents prior to and during the ZnO deposition. Superficial Cu2O to CuO oxidation was identified as a limiting factor to heterojunction quality due to recombination at the ZnO/Cu2O interface. Optimization of AP-SALD conditions as well as keeping Cu2O away from air and moisture in order to minimize Cu2O surface oxidation led to improved device performance. A three-fold increase in the open-circuit voltage (up to 0.65 V) and a two-fold increase in the short-circuit current density produced solar cells with a record 2.2% power conversion efficiency (PCE). This PCE is the highest reported for a Zn1-xMgxO/Cu2O heterojunction formed outside vacuum, which highlights atmospheric pressure spatial ALD as a promising technique for inexpensive and scalable fabrication of Cu2O-based photovoltaics.Cambridge Overseas and Commonwealth Trust, the Rutherford Foundation of New Zealand, Girton College CambridgeERC Advanced Investigator Grant, Novox [ERC-2009-adG247276]EPSRC [RGS3717

Size-Dependent Photon Emission from Organometal Halide Perovskite Nanocrystals Embedded in an Organic Matrix.

In recent years, organometal halide perovskite materials have attracted significant research interest in the field of optoelectronics. Here, we introduce a simple and low-temperature route for the formation of self-assembled perovskite nanocrystals in a solid organic matrix. We demonstrate that the size and photoluminescence peak of the perovskite nanocrystals can be tuned by varying the concentration of perovskite in the matrix material. The physical origin of the blue shift of the perovskite nanocrystals’ emission compared to its bulk phase is also discussed.D.D. acknowledges the Department of Physics, University of Cambridge and the KACST-Cambridge University Joint Centre of Excellence for financial support. G.L. thanks the Gates Cambridge Trust for support. Q.S. acknowledges the Imperial College Junior Research Fellowship. J.L.M.D. acknowledges ERC Advanced Investigator Grant, Novox, ERC-2009-adG247276. This work was supported by the Engineering and Physical Sciences Research Council, UK.This is the final published version. It first appeared at http://pubs.acs.org/doi/abs/10.1021/jz502615e

Engineering Schottky contacts in open-air fabricated heterojunction solar cells to enable high performance and ohmic charge transport.

The efficiencies of open-air processed Cu2O/Zn(1-x)Mg(x)O heterojunction solar cells are doubled by reducing the effect of the Schottky barrier between Zn(1-x)Mg(x)O and the indium tin oxide (ITO) top contact. By depositing Zn(1-x)Mg(x)O with a long band-tail, charge flows through the Zn(1-x)Mg(x)O/ITO Schottky barrier without rectification by hopping between the sub-bandgap states. High current densities are obtained by controlling the Zn(1-x)Mg(x)O thickness to ensure that the Schottky barrier is spatially removed from the p-n junction, allowing the full built-in potential to form, in addition to taking advantage of the increased electrical conductivity of the Zn(1-x)Mg(x)O films with increasing thickness. This work therefore shows that the Zn(1-x)Mg(x)O window layer sub-bandgap state density and thickness are critical parameters that can be engineered to minimize the effect of Schottky barriers on device performance. More generally, these findings show how to improve the performance of other photovoltaic system reliant on transparent top contacts, e.g., CZTS and CIGS.This work was supported by EPSRC of the UK (award number RG3717)This is the accepted manuscript. The final version is available from ACS at http://pubs.acs.org/doi/abs/10.1021/am5058663