The Synthesis and Characterization of Colloidal Nanocrystals for Perovskite Solar Cells

Abstract

In recent times, the emergence of organic-inorganic halide perovskite materials have been considerable attention to many scientists in photovoltaic fields due to high light absorption coefficient, outstanding charge carriers diffusion length and optical band gap as light absorbers. Herein, we have applied colloidal quantum dots to hole-conducting layers in methylammonium lead triiodide-based perovskite solar cells. First, we use lead sulfide(PbS), colloidal quantum dots(QDs) which are synthesized by hot-injection method due to low-cost, solution-processable materials, strong absorption coefficient and size-dependent optical properties compared to expensive organic-conducting materials. They are spin-coated on mesoscopic perovskite layers to form n-i-p junctions. The devices with different optical band gaps of PbS QDs show slightly enhanced current density contrary to reduced open-circuit voltages than hole-free perovskite solar cells. The maximum power conversion efficiency has reached 6.7% with PbS QDs. We also synthesized Au-PbS core-shell structures for the hole-transporting layer due to strong p-type doping effect resulting in enhanced hole transfer and the relation between plasmon from cores and excitons from shells. Furthermore, we have applied CZTS and CZTSe QDs composed of quaternary Copper-Zinc-Tin-Sulfur or Selenium compounds to hole transport layer for enhancing the photovoltaic performances and tuning band gaps of perovskite solar cells. CZTS and CZTSe QDs with diameters of 10 to 20nm were also synthesized by hot-injection method and when they are spin-coated on the absorber layer solar cell devices show higher current density, open-circuit voltage and IPCE than hole-conducting materials free perovskite solar cell. Their maximum power conversion efficiency has been over 7% and open-circuit voltage has been changed depending on particle’s compositions. ⓒ 2016 DGIST