Recent progress in the development of hole-transport materials to boost the power conversion efficiency of perovskite solar cells

Organic-inorganic hybrid systems are crystalline materials that showed significant advancement in many technological applications. Surprisingly, perovskite materials have been introduced as challengers to compete with the top photovoltaic technologies. Recently, power conversion efficiencies of the perovskite materials have jumped from 3% to the state-of-the-art laboratory photoconversion efficiency of 26%. To reach the optimum performance of the perovskite solar cells, researchers need to identify the highest performance fabrication techniques and device structures. Herein, we highlight the best hole transport materials that have been used to achieve the highest performance upon their use in perovskite solar cell devices in the last decade. Besides, several fabrication techniques, operating mechanisms, and device structures are summarized and discussed. This review presents a brief look on the advancement in the field of perovskite solar cells and how to achieve the best performance via adjusting the hole transport material.