Composition engineering of a Cu2ZnGexSn1−xS4 nanoparticle hole transport layer for carbon electrode-based perovskite solar cells.

Cu₂ZnSnS₄ (CZTS) and Cu₂ZnGeS₄ (CZGS) nanoparticles are important inorganic hole transport layers (HTLs) for carbon electrode-based perovskite solar cells (C-PSCs). However, the performances of the corresponding C-PSCs are still not satisfactory, which mainly originates from the un-optimized photoelectronic properties of the pristine CZTS and CZGS nanoparticles. Herein, composition engineering via alloying CZTS and CZGS is used to optimize the photo-electronic properties of the resulting CZG_xT_1−xS HTLs (x = 0, 0.25, 0.50, 0.75, and 1.0), and when combined with a FA_1−xMA_xPbI_3−yBr_y active layer, the performance of the C-PSCs was greatly increased. The optimum HTL of CZG_0.5T_0.5S exhibits a suitable conduction band energy barrier at the perovskite/CZG_0.5T_0.5S interface, and thus, charge carrier recombination at the perovskite/CZG_0.5T_0.5S interface is effectively suppressed. However, the CZG_0.5T_0.5S HTL exhibited much greater conductivity, which efficiently transported the holes from the perovskite to a carbon electrode. This resulted in C-PSCs with the CZG_0.5T_0.5S HTL demonstrating a champion power conversion efficiency of 19.8%. [ABSTRACT FROM AUTHOR]