SnS Homojunction Solar Cell with n‐Type Single Crystal and p‐Type Thin Film

Herein, a pn homojunction SnS solar cell is fabricated for the first time by the deposition of p‐type SnS polycrystalline thin films on the recently reported large n‐type SnS single crystals. The p‐type thin films consist of columnar grains that grow along the <100> direction, which is the same orientation as the n‐type single crystal. In addition, the interface of the pn homojunctions is void‐free and compositionally sharp. The SnS homojunction solar cell achieves an open‐circuit voltage ( V OC ) of 360 mV, which is as large as the highest V OC of previously reported SnS‐based heterojunction solar cells. The built‐in potential of the homojunction cell is 0.92 eV, which is close to the bandgap energy of SnS (≈1.1 eV), and larger than reported for heterojunctions (≈0.7 eV). The resulting 1.4% conversion efficiency ( η ) of the homojunction solar cell is smaller than the record 4–5% in heterojunctions, mainly due to the low short‐circuit current density ( J SC ) of 7.5 mA cm −2 . Once the device structure of the homojunction cell is optimized to efficiently collect the photogenerated carriers and achieve a comparable J SC as the conventional heterojunction cells (≈25 mA cm −2 ), high η exceeding 4–5% will be realized with improving the V OC .