All-polymer solar cells (all-PSCs) exhibiting superior device stability and mechanical robustness have attracted considerable interest. Emerging polymerized small-molecule acceptors (PSMAs) have promoted the progress of all-PSCs exceeding a power conversion efficiency (PCE) of 14%. However, most of the all-PSCs are processed with halogenated solvents that are hazardous towards humans and the environment. Herein, halogen-free processing solvents of CS₂, 1,2,4-TMB and o-XY are utilized for producing eco-friendly and highly efficient all-PSCs. In particular, o-XY solvent-processed all-PSCs achieve a high PCE of 15.6%, which is among the highest values in green-solvent-processed all-PSCs to date. Detailed investigations reveal that such enhancement is mainly attributed to the optimal blend morphology and polymer crystalline structures, which is resulted from aggregated structures of polymers formed in o-XY. Importantly, o-XY-processed-all-PSCs are successfully fabricated in ambient conditions, affording a high PCE approaching 15.0%. This work highlights the importance of green solvent strategy in controlling the polymer aggregated structures and blend film morphology of all-PSCs, paving the way towards high-performance and eco-friendly all-PSCs for practical applications.

Y6 is a new type of non-fullerene acceptor, which has led to power conversion efficiencies of single-junction polymer solar cells over 17% when combined with a careful choice of polymeric donors. However, the excited state characteristics of Y6, which is closely correlated with its opto-electronic applications, are not clear yet. In this work, we studied the excited state properties of the Y6 solution and Y6 film, by using steady-state and time-resolved spectroscopies as well as time-dependent density functional theory (TD-DFT) calculations. UV-Vis absorption and fluorescence simulation, natural transition orbitals (NTOs) and hole-electron distribution analysis of Y6 solution were performed for understanding the excitation properties of Y6 by using TD-DFT calculations. The lifetimes of the lowest singlet excited state in Y6 solution and film were estimated to be 0.98 and 0.8 ns, respectively. Combining the exciton lifetime and photoluminescence (PL) quantum yield, the intrinsic radiative decay lifetimes of Y6 in the solution and film were estimated, which were 1.3 and 10.5 ns for the Y6 solution and film, respectively. Long exciton lifetime (~0.8 ns) and intrinsic radiative decay lifetime (~10.5 ns) of Y6 film enable Y6 to be a good acceptor material for the application of polymer solar cells.

Polythiophenes are the most promising electron donors for organic solar cells (OSCs) in large-scale manufacturing owing to their simple chemical structures and low production costs. However, the efficiency of polythiophene solar cells is largely limited because of the difficulty in morphology optimization. Herein, we report the construction of a refined fibril network structure in polythiophene:non-fullerene acceptor blends based on the classical nucleation theory. By screening solvents for polythiophene to obtain an appropriate nucleation driving force while ensuring that the non-fullerene acceptor does not over-crystallize, a refined crystalline fibril network morphology was obtained in the blend consisting of a structurally simple polythiophene P5TCN-HD and a non-fullerene acceptor. This optimal morphology improved exciton dissociation and charge transport, thereby endowing the solar cells with an unprecedented power conversion efficiency of 18.12% and a fill factor of 79.17%, marking new breakthroughs for polythiophene-based OSCs. Notably, these results were achieved using toluene as the solvent, which is a common non-halogenated and environmentally benign solvent. Moreover, the crucial impact of solvent quality on the formation of the fibril network structure was revealed, offering valuable insights for optimizing the morphology of polythiophene systems. This underscores the promising prospect of polythiophenes in developing high-efficiency yet low-cost OSCs via environmentally benign processing, driving the industrialization of OSCs.

As a classical polymer acceptor material, N2200 has received extensive attention and research in the field of polymer solar cells (PSCs). However, the intrinsic properties of ground- and excited-states in N2200, which are critical for the application of N2200 in PSCs, remain poorly understood. In this work, the ground- and excited-state properties of N2200 solution and film were studied by steady-state and time-resolved spectroscopies as well as time-dependent density functional theory (TD-DFT) calculations. The transition mechanism of absorption peaks of N2200 was evaluated through the natural transition orbitals (NTOs) and hole–electron population analysis by TD-DFT. Time-resolved photoluminescence (TRPL) study shows that the lifetimes of singlet excitons in N2200 chlorobenzene solution and film are ∼90 ps and ∼60 ps, respectively. Considering the absolute quantum yield of N2200 film, we deduce that the intrinsic lifetime of singlet exciton can be as long as ∼20 ns. By comparing the TRPL and transient absorption (TA) kinetics, we find that the decay of singlet excitons in N2200 solution is dominated by a fast non-radiative decay process, and the component induced by intersystem crossing is less than 5%. Besides that, the annihilation radius, annihilation rate and diffusion length of singlet excitons in N2200 film were evaluated as 3.6 nm, 2.5 × 10⁻⁹ cm³ s⁻¹ and 4.5 nm, respectively. Our work provides comprehensive information on the excited states of N2200, which is helpful for the application of N2200 in all-PSCs.

As one of the successful approaches to GaAs surface passivation, wet-chemical nitridation is applied here to relate the effect of surface passivation to carrier recombination processes in bulk GaAs. By combining time-resolved photoluminescence and optical pump – THz probe measurements we found that surface hole trapping dominates the decay of photoluminescence, while photoconductivity dynamics is limited by surface electron trapping. Compared to untreated sample dynamics, the optimized nitridation reduces hole and electron trapping rate by at least 2.6 and 3 times, respectively. Our results indicate that under ambient conditions recovery of the fast hole trapping due to the oxide regrowth at the deoxidized GaAs surface takes tens of hours while it is effectively inhibited by surface nitridation. Our study demonstrates that surface nitridation stabilizes GaAs surface via reduction of both electron and hole trapping rates, which results in chemical and electronical passivation of bulk GaAs surface.