Rotational design of charge carrier transport layers for optimal antimony trisulfide solar cells and its integration in tandem devices

Sb2S3 thin-film solar cells have recently gained attention due to their low cost, low toxicity, and simple fabrication. However, there is still plenty of room to improve their performance. It is known that efficient carrier transport is essential for high performance Sb2S3 solar cells, which, unfortunately, is difficult to characterize by conventional testing methods. Therefore, the carrier transport process in Sb2S3 solar cells was studied here using a theoretical simulation. The results show that high solar performances can be achieved with a wide parameter window for selecting the electron transport layer as well as the hole transport layer, viz., with a conduction band minimum of the electron transport layer (-4.4 eV < CBM < -3.2 eV), and a valence band maximum of the hole transport layer (-5.2 eV > VBM > -6.4 eV). Here the interfacial potential barrier become negligible and as a consequence electrons and holes cross at ease, which guarantee the good device performance. Indeed, a Sb2S3 solar cell with a high power conversion efficiency (PCE) can be obtained by ensuring that the carrier transport and collection are unimpeded in the device, i.e., the Sb2S3-based single junction solar cells shows high efficiency of 19.53%. Furthermore, we found that optimized Sb2S3 solar cells are particularly suitable for use as the top cell of tandem structure solar cells. Thus, a Sb2S3/Sb2Se3 double junction solar cell structure was proposed. With a 0.5 mu m thick Sb2S3 absorber, double junction solar cells could achieve a theoretical efficiency as high as 26.64%. Our results based on the rotational design of bandgap alignment provide a general guide rule for selecting the optimal electron transport layer as well as the hole transport layer to boost the power conversion efficiency for Sb2S3 solar cells up to its theoretical limit.