SnS is a promising earth-abundant material for photovoltaic applications. Heterojuction solar cells were made by vapor deposition of p-type tin(II) sulfide, SnS, and n-type zinc oxysulfide, Zn(O,S), using a device structure of soda-lime glass/Mo/SnS/Zn(O,S)/ZnO/ITO. A record efficiency was achieved for SnS-based thin-film solar cells by varying the oxygen-to-sulfur ratio in Zn(O,S). Increasing the sulfur content in Zn(O,S) raises the conduction band offset between Zn(O,S) and SnS to an optimum slightly positive value. A record SnS/Zn(O,S) solar cell with a S/Zn ratio of 0.37 exhibits short circuit current density (Jsc), open circuit voltage (Voc), and fill factor (FF) of 19.4 mA/cm2, 0.244 V, and 42.97%, respectively, as well as an NREL-certified total-area power-conversion efficiency of 2.04% and an uncertified active-area efficiency of 2.46%.

The formation of a two-dimensional electron gas (2-DEG) using SrTiO3 (STO)-based heterostructures provides promising opportunities in oxide electronics. We realized the formation of 2-DEG using several amorphous layers grown by the atomic layer deposition (ALD) technique at 300 °C which is a process compatible with mass production and thereby can provide the realization of potential applications. We found that the amorphous LaAlO3 (LAO) layer grown by the ALD process can generate 2-DEG (∼1 × 1013/cm2) with an electron mobility of 4–5 cm2/V·s. A much higher electron mobility was observed at lower temperatures. More remarkably, amorphous YAlO3 (YAO) and Al2O3 layers, which are not polar-perovskite-structured oxides, can create 2-DEG as well. 2-DEG was created by means of the important role of trimethylaluminum, Me3Al, as a reducing agent for STO during LAO and YAO ALD as well as the Al2O3 ALD process at 300 °C. The deposited oxide layer also plays an essential role as a catalyst that enables Me3Al to reduce the STO. The electrons were localized very near to the STO surface, and the source of carriers was explained based on the oxygen vacancies generated in the STO substrate.

We demonstrate a tunable electron-blocking layer to enhance the performance of an Earth-abundant metal-oxide solar-cell material. A 5 nm thick amorphous ternary metal-oxide buffer layer reduces interface recombination, resulting in sizable open-circuit voltage and efficiency enhancements. This work emphasizes the importance of interface engineering in improving the performance of Earth-abundant solar cells. Thin lm solar cells comprising Earth-abundant, non-toxic, and air-stable materials represent a promising class of photovoltaic (PV) devices compatible with terawatts-scale deployment. 1-3 Cuprous oxide (Cu 2 O) is one of several candidate materials under consideration with the potential to reach 20% power conversion efficiency. 4,5 Doping this material to make it n-type has proven to be challenging, thus a common PV device architecture comprises a Cu 2 O-ZnO heterojunction structure. However, device efficiencies remain low, with wafer-based Cu 2 O devices (by thermal oxidation of Cu sheets at $1010 C) reaching 4.1% (ref. 6) and thin lm Cu 2 O devices (by electrochemical deposition) reaching 1.3% (ref. 7). The open-circuit voltage (V OC) of these devices is signicantly below the theoretical limit of Cu 2 O, due to a low built-in potential caused by non-ideal band alignment between the absorber and transparent conducting oxide (TCO), and a high recombination-current driven by interface-traps. 8,9 To mitigate the latter voltage-loss mechanism, we introduce a thin ($5 nm) buffer layer between the absorber and the TCO. This layer serves as an electron-blocking layer, reducing the magnitude of the recombination current at the absorber-TCO interface. This approach is reminiscent of the Si-based heterojunction with intrinsic thin layer (HIT) devices, which exhibit V OC superior to the best Si homojunction devices by creating a small energy barrier with a low density of interface-traps. 10 This energy barrier is expressed as a conduction-band offset (DE CB) of the buffer layer relative to the absorber layer; DE CB must be carefully "tuned" to avoid current losses (stemming from too high DE CB) or voltage losses (stemming from a negative DE CB). 11 This tunability can be achieved by using ternary compounds for the buffer layer, whereby the ratio of two cations (anions) typically modies the conduction (valence) band position. 12,13 Judicious composition selection of this ternary compound allows one to simultaneously limit the concentrations of carriers at the interface as well as reduce the interface-trap density, which reduces dark saturation current density (J 0) and increases V OC. To achieve maximum benet, this layer needs to