Antimony Selenide Thin Film Solar Cells with an Electron Transport Layer of Alq_3

We fabricated Sb_2Se_3 thin film solar cells using tris(8-hydroxy-quinolinato) aluminum (Alq_3) as an electron transport layer by vacuum thermal evaporation. Another small organic molecule of N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine (NPB) was used as a hole transport layer. We took ITO/NPB/Sb_2Se_3/Alq_3/Al as the device architecture. An open circuit voltage (V_\rm oc) of 0.37 V, a short circuit current density (J_\rm sc) of 21.2 mA/cm^2, and a power conversion efficiency (PCE) of 3.79% were obtained on an optimized device. A maximum external quantum efficiency of 73% was achieved at 600 nm. The J_\rm sc, V_\rm oc, and PCE were dramatically enhanced after introducing an electron transport layer of Alq_3. The results suggest that the interface state density at Sb_2Se_3/Al interface is decreased by inserting an Alq_3 layer, and the charge recombination loss in the device is suppressed. This work provides a new electron transport material for Sb_2Se_3 thin film solar cells.