Ways to Improve the Performance of Triple-Mesoscopic Hole-Conductor-Free Perovskite-Based Solar Cells

Hybrid perovskite is an attractive semiconductor material being used intensively in photovoltaic cells for the last 10 years. It can be integrated in several architectures of solar cells, which are based on the concept that the perovskite is sandwiched between an electron selective contact and a hole-selective contact capped by a metal electrode as the back contact. An additional and unique solar cell structure is the mesoporous layers solar cell, which is based on mesoporous TiO₂ following by mesoporous ZrO₂ (or Al₂O₃) and capped by mesoporous carbon or recently by mesoporous indium tin oxide (ITO) electrodes. These solar cells are fabricated by screen printing and the perovskite is applied in the last step by infiltration through the three mesoporous layers. This solar cell structure holds a great promise, due to its fabrication techniques, high stability, and recycling process. In this review, several ways are brought together to improve the performance of these cells, using additives for the different layers, posttreatments, and ways to change the energy level positions to enhance the photovoltaic performance. Also, a new concept of replacing the carbon with a mesoporous ITO electrode is presented, which shows promising results. The review ends with summary and outlook.