K. D. G. Imalka Jayawardena

Self-assembled monolayers (SAMs) are a popular choice for achieving high-efficiency perovskite solar cells (PSCs). However, the incomplete wetting of the perovskite on (4-(3,6-dimethyl-9H-carbazol-9-yl)butyl)phosphonic acid (Me-4PACz) SAMs in PSCs has proven to be a challenge. Recently, the use of surface modifiers such as alumina nanoparticles and poly(9,9-bis(3′-(N,N-dimethyl)-N-ethylammonium-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene))dibromide (PFN–Br) has been demonstrated to eliminate this bottleneck. However, the influence of these surface modifiers on device stability has not been reported. Here, we studied the influence of alumina nanoparticles and PFN–Br on Me-4PACz device stability when stressed under ISOS-D-2I and ISOS-D-2 conditions (at 65 °C). The use of alumina nanoparticles leads to efficient scavenging of iodine, improved bulk electrical and surface electronic homogeneity in fresh films, which is preserved even when the films are degraded, and the formation of 2D perovskites, which act as a barrier against moisture induced degradation. In comparison, perovskites based on PFN–Br show a distinct lack of similar characteristics for fresh and degraded samples. This allows the realisation of alumina modified Me-4PACz based PSCs with a tenfold improved T80 lifetime of 1530 h under ISOS-D-2 conditions compared to the PFN–Br based device stack. Our study uncovers a new approach towards enhancing PSC stability, which could potentially be applied under more strenuous ISOS test conditions to further improve device stability.

Managing iodine formation is crucial for realising efficient and stable perovskite photovoltaics. Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is a widely adopted hole transport material, particularly for perovskite solar cells (PSCs). However, Improving the performance and stability of PEDOT:PSS based perovskite optoelectronics remains a key challenge. We show that amine-containing organic cations de-dope PEDOT:PSS, causing performance loss, which is partially recovered with thiocyanate additives. However, this comes at the expense of device stability due to cyanogen formation from thiocyanate-iodine interaction which is accelerated in the presence of moisture. To mitigate this degradation pathway, we incorporate an iodine reductant in lead-tin PSCs. The resulting devices show an improved power conversion efficiency of 23.2% which is among the highest reported for lead-tin PSCs, and ~66% enhancement for the T_S80 lifetime under maximum power point tracking in ambient conditions. These findings offer insights for designing next-generation hole extraction materials for more efficient and stable PSCs.

Organic semiconductors are a promising material candidate for X‐ray detection. However, the low atomic number (Z) of organic semiconductors leads to poor X‐ray absorption thus restricting their performance. Herein, the authors propose a new strategy for achieving high‐sensitivity performance for X‐ray detectors based on organic semiconductors modified with high –Z heteroatoms. X‐ray detectors are fabricated with p‐type organic semiconductors containing selenium heteroatoms (poly(3‐hexyl)selenophene (P3HSe)) in blends with an n‐type fullerene derivative ([6,6]‐Phenyl C71 butyric acid methyl ester (PC₇₀BM). When characterized under 70, 100, 150, and 220 kVp X‐ray radiation, these heteroatom‐containing detectors displayed a superior performance in terms of sensitivity up to 600 ± 11 nC Gy⁻¹ cm⁻² with respect to the bismuth oxide (Bi₂O₃) nanoparticle (NP) sensitized organic detectors. Despite the lower Z of selenium compared to the NPs typically used, the authors identify a more efficient generation of electron‐hole pairs, better charge transfer, and charge transport characteristics in heteroatom‐incorporated detectors that result in this breakthrough detector performance. The authors also demonstrate flexible X‐ray detectors that can be curved to a radius as low as 2 mm with low deviation in X‐ray response under 100 repeated bending cycles while maintaining an industry‐standard ultra‐low dark current of 0.03 ± 0.01 pA mm⁻².

The development of perovskite solar cells (PSCs) with low recombination losses at low processing temperatures is an area of growing research interest as it enables compatibility with roll‐to‐roll processing on flexible substrates as well as with tandem solar cells. The inverted or p–i–n device architecture has emerged as the most promising PSC configuration due to the possibility of using low‐temperature processable organic hole‐transport layers and more recently, self‐assembled monolayers such as [4‐(3,6‐dimethyl‐9H‐carbazol‐9‐yl)butyl]phosphonic acid (Me‐4PACz). However, devices incorporating these interlayers suffer from poor wettability of the precursor leading to pin hole formation and poor device yield. Herein, the use of alumina nanoparticles (Al₂O₃ nanoparticles (NPs)) for pinning the perovskite precursor on Me‐4PACz is demonstrated, thereby improving the device yield. While similar wettability enhancements can also be achieved by using poly[(9,9‐bis(3′‐((N,N‐dimethyl)‐N‐ethylammonium)‐propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)]dibromide (PFN‐Br), a widely employed surface modifier, the incorporation of Al₂O₃ NPs results in significantly enhanced Shockley–Read–Hall recombination lifetimes exceeding 3 μs, which is higher than those on films coated directly on Me‐4PACz and on PFN‐Br‐modified Me‐4PACz. This translates to a champion power conversion efficiency of 19.9% for PSCs fabricated on Me‐4PACz modified with Al₂O₃, which is a ≈20% improvement compared to the champion device fabricated on PFN‐Br‐modified Me‐4PACz.

Pb‐Sn mixed perovskites are becoming increasingly popular as narrow‐bandgap (1.2–1.3 eV) light absorbers in single‐junction perovskite solar cells (PSCs) and as bottom cells for all‐perovskite tandem solar cells, for high‐efficiency, low‐cost, lightweight, roll‐to‐roll printable photovoltaic (PV) applications. From the first report of planar Pb:Sn mixed PSCs in 2014, the power conversion efficiencies (PCE) have increased from 10% to 21% by the end of 2020 with an exponential growth in research conducted in this field. Despite much effort, the performance and stability of Pb‐Sn mixed PSCs are still limited, which constrains their long‐term use in all‐perovskite tandem devices. This review highlights the avenues explored in improving different aspects of Pb‐Sn mixed PSCs and provides a comprehensive discussion of the interdependent factors affecting the device performance. This includes compositional engineering of the perovskite crystal, absorber layer fabrication and crystallization methods, bandgap tuning, Sn⁴⁺ reduction, and surface passivation of the absorber layer, as well as the selection of interlayers and electrodes of the final PSC.

Cs incorporation into perovskite filmviaa thin Cs₂CO₃layer ETL passivation treatment.