Dopant-free carrier-selective contacts are becoming increasingly attractive for application in silicon solar cells because of the depositions for their fabrication being simpler and occurring at lower temperatures. However, these contacts are limited by poor thermal and environmental stability. In this contribution, the use of the conductive high work function of cuprous iodide, with its characteristic thermal and ambient stability, has enabled a hole-selective contact for p-type silicon solar cells because of the large conduction band offset and small valence offset at the CuI/p-Si interface. The contact resistivity (≈30 mΩ•cm 2 ) of the Ag/CuI (20 nm)/p-Si contact after annealing to 200 °C represents the CuI-based hole-selective contact with low resistance and high thermal stability. Microscopic images and elemental mapping of the Ag/CuI/p-Si contact interface revealed that a nonuniform, continuous CuI layer separates the Ag electrode and p-type Si. Thermal treatment at 200 °C results in the intermixing of the Ag and CuI layers. As a result, the 200 °C thermal process improves the efficiency (20.7%) and stability of the p-Si solar cells featuring partial CuI hole-selective contact. Furthermore, the devices employing the CuI/Ag contact are thermally stable upon annealing to temperatures up to 350 °C. These results not only demonstrate the use of metal iodide instead of metal oxides as hole-selective contacts for efficient silicon solar cells but also have important implications regarding industrial feasibility and longevity for deployment in the field.

Dopant‐free carrier‐selective contacts have attracted considerable research interests, extensively due to the avoidance of high‐temperature doping and their simple, environmental‐friendly fabrication processes for crystalline silicon (c‐Si) solar cells. Herein, a novel dopant‐free electron‐selective material, europium fluoride (EuF x ) is developed. A desired Ohmic contact can be formed between lightly doped n‐type c‐Si and aluminum (Al) by inserting nanoscale EuF x films (2–4 nm) through thermal evaporation so as to avoid the high‐temperature phosphorus diffusion and offer a simple, robust process. The contact resistivity is lower than 20 mΩ cm2. EuF x film can effectively select electrons and block holes at the contact interface, which is attributed to its low work function and a large valence band offset with respect to n‐type c‐Si. Combined with an ultrathin silicon oxide (SiO2) as a passivation layer, a champion power conversion efficiency 21.6% of n‐type c‐Si solar cells with full‐area SiO2/EuF x is achieved. An average of absolute efficiency is increased by 12% compared with the reference. The results show that EuF x has particularly excellent electron‐selective transport performance. The new possibility of using lanthanide salts as electron‐selective contacts for photovoltaic (PV) devices is set up.

Dopant‐free carrier‐selective contacts have drawn intensive attention for efficient crystalline silicon (c‐Si) photovoltaics due to the low‐temperature simple process and better carrier selectivity. By incorporating a thermally evaporated dielectric film cerium fluoride (CeF3) as the electron transport layer (ETL) between a c‐Si(n) and aluminum (Al) electrode, higher conversion efficiency of the crystalline silicon solar cell is obtained, which is 21.27% compared to 16.89% of a reference cell without CeF3. The insertion of an ultrathin CeF3 ETL helps in alleviating the strong Fermi‐level pinning at the interface, leading to better electron transport with a low contact resistivity of 10.96 mΩ cm2. The morphology and element distribution of the interface are also investigated by high‐resolution transmission electron microscopy (HRTEM). The primary results demonstrate that the utilization of kinds of lanthanide fluorides, including CeF3, offers a good choice for efficient and cost‐effective electron‐selective contacts for optical–electrical devices.

Most crystalline silicon (c‐Si) solar cells are based on high temperature–processed p‐n junctions or highly doped heterojunctions. The concept of dopant‐free carrier selective contact has become a research hotspot and been successfully demonstrated with n‐type Si wafers, showing the great potential of simplified fabrication process and lower thermal‐consuming. However, there are few successful cases on p‐Si, dopant‐free p‐Si/CdS (cadmium sulfide)/ITO (indium tin oxide) solar cells with champion efficiency of 12.29% (device area 4 cm2) have been demonstrated with DC magnetron sputtered CdS thin films working as electron‐selective contact. A proper annealing treatment is found essential in improving the p‐Si/CdS/ITO heterocontact and device performance. The author's preliminary results confirm the feasibility of preparation of efficient p‐Si wafer–based dopant‐free solar cells.

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