This review provides an overview of factors affecting film morphology and how together with device architecture they impact perovskite cell performance.

Three novel hole-conducting molecules (T101, T102 and T103) based on a triptycene core have been synthesized using short routes with high yields. The optical and electrochemical properties were tuned by modifying the functional groups, through linking the triptycene to diphenylamines via phenyl and/or thienyl groups. The mesoporous perovskite solar cells fabricated using T102 and T103 as the hole transporting material (HTM) showed a power conversion efficiency (PCE) of 12.24% and 12.38%, respectively, which is comparable to that obtained using the best performing HTM spiro-OMeTAD. The T102 based device showed higher fill factor (69.1%) and V_oc (1.03 V) than the spiro-OMeTAD based device (FF = 63.4%, V_oc = 0.976 V) whereas the T103 based device showed comparable J_sc (20.3 mA cm⁻²) and higher V_oc (0.985 V) than the spiro-OMeTAD (J_sc = 20.8 mA cm⁻²) based cell.

Power conversion efficiency (PCE) of the perovskite solar cells (PSCs) has remarkably been increased from 3.1% to 25.2%. The fast expansion of the PSCs has been along with the development of compositional and interface engineering, which has been playing a critical role. For the PSCs with record high-efficiency and stability, the perovskite absorber layer has been changed from the initial MAPbI3- to FAPbI3-based compositions. Owing to the enormous engineering works, perovskite absorber layers with monolithic grains could be achieved, in which the interior defects are negligible compared with the surface defects. Therefore, interface engineering, which can passivate the surface defects and/or isolate the perovskite from the environmental moistures, has been playing a more and more important role to further boost the PCE and stability of the PSCs. Herein, a compact review study of the compositional and interface engineering is presented and promising strategies and directions of the PSCs are discussed.

Organic–inorganic halide perovskite solar cells (PSCs) have become one of the most exciting fields in the search for renewable energy sources with the power conversion efficiency (PCE) of PSCs having increased in only a few years from less than 5% to certified values of over 22%. To obtain high efficiencies in PSCs hole transporting materials (HTMs) are needed, and the HTM used in the best devices is so expensive as to make them potentially uncompetitive. In this review we give an overview of the types of HTMs that have been developed and discuss some of the strategies that have been used in designing HTMs for efficient PSCs, including the apparent effects of functional groups in and structures of organic HTMs on device parameters such as the PCE, fill factor (FF), open circuit voltage (V_oc), and the stability of the resulting PSCs. We suggest some tentative design principles that might enable the rational design of a cost-effective HTM for efficient PSCs.