A research group led by Prof. LIU Shengzhong from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) and Prof. YANG Dong at Shaanxi Normal University developed the high efficiency semi-transparent perovskite solar cells by using MoO₃ sandwiched gold nanomesh (MoO₃/Au/MoO₃) multilayer as the transparent electrode. Combined with a superior heterojunction silicon solar cell, a high efficiency four-terminal perovskite/silicon tandem solar cell was obtained. Their findings were published in Advanced Functional Materials.

 Device structure of the semi-transparent perovskite cell with ultra-thin gold nanonet as transparent electrode (Top). Photograph of the semi-transparent device (Left). J-V characteristic of the semitransparent perovskite top cell (red line) , the silicon bottom cell (blue line) and the silicon cell works indepently (black line) (Right). (Image by DUAN Lianjie and WANG Ziyu) 

The crystalline Si-based solar cells have been dominating the ever-expanding global photovoltaic (PV) market with about 95% market share. With the cell efficiency reaching its theoretical limit of 26.6%, there is little hope to further raise its performance by device optimization within the single-junction cell architecture.

Tandem/multijunction structure has been proven to be an effective way to break the Shockley-Queisser limit. To obtain a high efficiency tandem solar cell, the key is to fabricate transparent electrode with high cinductivity as well as high transparency through a mild method.

To obtain the high conductive and high transparent transparent electrode, the group demonstrated a MoO₃/Au/MoO₃ multilayer fabricated by thermal evaporation. The thermal evaporation is mild and will not damage the underneath layer.

The large surface tension of MoO₃ improves wettability for gold, resulting in Frank–van der Merwe growth to produce an ultrathin gold nanomesh layer, which guarantees not only excellent conductivity but also great optical transparency. The top MoO₃ layer reduces the reflection at the gold layer to further increase light transmission.

As a result, the semitransparent perovskite cell shows an efficiency of 18.3%, the highest reported for this type of devices. When the semitransparent perovskite device is mechanically stacked with a heterojunction silicon solar cell of 23.3% PCE, it yields a combined efficiency of 27.0%, higher than those of both the sub-cells. This breakthrough in elevating the efficiency of semitransparent and multijunction/tandem devices can help to break the Shockley–Queisser limit.