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.