Hole Transport Materials in Conventional Structural (n–i–p) Perovskite Solar Cells: From Past to the Future

Abstract

With the application of organic–inorganic hybrid perovskites to liquid‐type solar cells, the unprecedented development of perovskite solar cells (Per‐SCs) has been boosted by the introduction of solid‐state hole transport materials (HTMs). The removal of liquid electrolyte has lead to improved efficiency and stability. Supported by high‐quality perovskite films, the certified efficiency of Per‐SCs has reached 25.2%. For Per‐SCs assembled in a conventional structure (n–i–p), the hole transport layer (HTL) plays an extra role in preventing the perovskite layer from external stimuli. In summary, the successful design and fabrication of the HTL must meet various requirements in terms of solubility, hole transport, recombination prevention, stability, and reproducibility, to name but a few. Many research strategies are focused on the development of high‐performance HTMs to meet such requirements. Such strategies for the development of HTMs employed in conventional n–i–p solar cells are reviewed herein. A vision of the future HTMs is proposed in this review based on the already proposed solutions and current trends.

Minimizing Voltage Losses in Perovskite Solar Cells

“…Along with the rapid progress of perovskite PV technology, a number of review works have pinpointed the critical aspects in reducing the PV performance losses of PSCs, such as interfacial passivation, [ 30–32 ] additive engineering, [ 33,34 ] precursor chemistry, [ 35–37 ] charge transport materials, [ 38,39 ] and so forth. However, very limited effort has been endeavored to unravel the origins of voltage losses and highlight the importance of high V oc in PSCs.…”

Strong electron acceptor additive based spiro-OMeTAD for high-performance and hysteresis-less planar perovskite solar cells

“…9 The hole transport layer (HTL), a crucial constituent of PSCs, is inserted between the perovskite absorber lm and the electrode. 10,11 Excellent HTLs can not only offer a route for transporting holes and blocking electrons, but also play as a layer of protection to inhibit oxygen and moisture from deteriorating the perovskite lms. [12][13][14] Among the various HTMs, the state-ofthe-art spiro-OMeTAD is intensively applied as the predominant HTM for highly efficient PSCs, due to its appropriate energy level, low glass-transition temperature and superior solution processability.…”

A Review on Solution‐Processable Dopant‐Free Small Molecules as Hole‐Transporting Materials for Efficient Perovskite Solar Cells

“…Although many well discussed reviews on dopant-free organic HTMs have been published, [66][67][68][69] the review here will specially center on these highly efficient small molecular HTMs (SM-HTMs) with PCEs of over 15% based on the classification of their molecular structures, which is quite different from the previous ones mainly cataloging the HTMs according to their device configurations. In this review, we will first investigate the properties of the solution processed dopantfree SM-HTMs and their relation to the molecular structures.…”