Researchers connected to Chinese flexible-perovskite maker SunFlex have published two separate papers within the same month, addressing two of the field's persistent stability problems: halide segregation in wide-bandgap perovskite/organic tandems, and desorption of the self-assembled monolayers (SAMs) used at the perovskite/electrode interface.
The first paper, from researchers at the Chinese Academy of Sciences and Shanghai Jiao Tong University - including SunFlex co-founder and CAS academician Yongfang Li - tackles a known weakness of wide-bandgap, high-bromide mixed-halide perovskites, which are used as the front cell in perovskite/organic tandem solar cells: they tend to mix unevenly during crystallization and undergo light-induced halide segregation during operation, both of which limit device performance. The team introduced a photo-transformable additive, 4-[3-(trifluoromethyl)-3H-diazirin-3-yl]benzylamine (TDB), into the perovskite precursor solution to address both problems in sequence. During crystallization, TDB suppresses the rapid precipitation of the bromide-rich phase and speeds up halide mixing during annealing, improving initial homogeneity. Then, once the device is under illumination, TDB itself transforms into a new chemical species that adsorbs more strongly onto the perovskite's grain-boundary surfaces, blocking the formation of iodide-related defects and suppressing both defect-assisted carrier trapping and ion migration - the mechanisms behind light-induced halide segregation.
Applied to a wide-bandgap perovskite cell (1.88 eV bandgap), the strategy produced a single-junction device with a power conversion efficiency (PCE) of 20.01%, an open-circuit voltage of 1.42 V, and a fill factor of 85.13%, along with improved stability under illumination. Built into a full monolithic perovskite/organic tandem cell, the technology reached a PCE of 28.80%, with a certified steady-state efficiency of 28.04%. The tandem retained 90% of its initial PCE after 625 hours of operation under the ISOS-L-1 stability testing protocol.
The second paper, from researchers at Soochow University, Southeast University and Hangzhou Dianzi University, addresses SAMs, which anchor to the transparent conductive oxide (TCO) substrate and form an interfacial dipole that helps extract charge carriers from the perovskite layer - a technique that has driven a series of efficiency gains in perovskite solar cells. The problem is that SAM molecules typically bond to the substrate only weakly, since their coordination sites have limited electron density, making them prone to desorbing under operational stress and compromising long-term stability. The team's solution was a new SAM built around a donor-acceptor-donor (D-A-D) resonant molecular structure, in which electronic resonance effects increase the negative charge density at the anchoring group, substantially strengthening the bond between its phosphonic acid group and the indium tin oxide (ITO) substrate and preventing desorption during operation.
Devices built with the new SAM showed negligible performance decay under maximum-power-point tracking at 85±5°C for 1,080 hours, retained over 93% of their initial efficiency after 1,080 hours under metal-halide lamp illumination (100 mW/cm², with 4.4% UV content) at 85±5°C, and retained over 98% of their initial efficiency after 720 thermal cycles between -40°C and 85°C. The same charge delocalization effect that strengthens the anchoring bond also improves carrier transport, and the devices reached certified efficiencies of 27.69% on small (0.063 cm²) rigid devices, 23.63% on a larger 15.64 cm² aperture area, and 26.64% on flexible substrates - the team highlighting that last result as evidence the approach works across both rigid and flexible device types.
Together, the two papers represent a significant show of research output for a single company-linked team within one month, following on from SunFlex's other recent moves, including a strategic partnership with aerospace company Nayuta Space to develop a 400 m² rollable flexible perovskite solar sail for satellites.
