Earth‐abundant Cu2BaSnS4 (CBTS) thin films exhibit a wide bandgap of 2.04–2.07 eV, a high absorption coefficient > 104 cm−1, and a p‐type conductivity, suitable as a top‐cell absorber in tandem solar cell devices. In this work, sputtered oxygenated CdS (CdS:O) buffer layers are demonstrated to create a good p–n diode with CBTS and enable high open‐circuit voltages of 0.9–1.1 V by minimizing interface recombination. The best power conversion efficiency of 2.03% is reached under AM 1.5G illumination based on the configuration of fluorine‐doped SnO2 (back contact)/CBTS/CdS:O/CdS/ZnO/aluminum‐doped ZnO (front contact).

Pe r o v sk it e so l a r c el l s, v a c u u m-d epo sit io n , el ec t r o n -s el ec t iv e l a y er , h o l e bl o c k in g l a y er , C 60 a n d C 70 (f u l l er en es )

Annealing in S vapor greatly improves the performance of electroplated Cu2 ZnSnS4 (CZTS) solar cells based on the bifacial configuration of Al-doped ZnO (AZO, front contact)/ZnO/CdS/CZTS/indium tin oxide (ITO, back contact), as compared to H2 S annealing in our previous works. S-vapor annealing does not cause severe damage to the conductivity of the ITO back contact. The highest device efficiency of 5.8 % was reached under 1 sun illumination from the AZO side. The well-preformed devices based on the ITO back contact demonstrate smaller series resistances and better fill factors, as compared to our substrate-type devices using Mo back contacts. An interfacial reaction at the ITO back contact has been revealed in experiments, which contributes to the formation of SnO2 -enriched interfacial layer and diffusion of In from ITO into CZTS through the Sn sites. Incorporation of In does not significantly change the optical and structural properties or the grain size of CZTS absorbers.

We report the properties of hybrid deposited iron pyrite (FeS 2) thin films applied as the back contact interface layers of CdS/CdTe solar cells. The hybrid deposition process for FeS 2 optimized in this study relies on DC magnetron sputtering of iron with simultaneous thermal evaporation of sulfur. We have fabricated solar cells incorporating CdS/CdTe window/absorber layers sputter-deposited onto commercial transparent conducting oxide coated glass and have compared the performance of devices incorporating the new FeS 2 /Cu/Au back contacts with that of standard devices incorporating Cu/Au back contacts. Considering our best devices of each type, the inclusion of the FeS 2 thin film as a hole transport layer has improved the open circuit voltage V OC by 2.1%, reaching 817 mV, and the fill-factor FF by 8.3% relative, reaching 74.7%, in comparison with devices omitting the FeS 2 layer. Under standard test conditions of 100 mA/cm 2 simulated AM1.5G and 25 C, devices utilizing the FeS 2 hole transport layer have shown a conversion efficiency  as high as 13.3%-a relative increase in of ~10% over our current laboratory standard back contact. The attained FF exceeds previous results for high efficiency sputter-deposited CdS/CdTe solar cells.

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