Efficient Semitransparent Organic Solar Cells with Tunable Color enabled by an Ultralow‐Bandgap Nonfullerene Acceptor

Semitransparent organic solar cells (OSCs) show attractive potential in power‐generating windows. However, the development of semitransparent OSCs is lagging behind opaque OSCs. Here, an ultralow‐bandgap nonfullerene acceptor, “IEICO‐4Cl”, is designed and synthesized, whose absorption spectrum is mainly located in the near‐infrared region. When IEICO‐4Cl is blended with different polymer donors (J52, PBDB‐T, and PTB7‐Th), the colors of the blend films can be tuned from purple to blue to cyan, respectively. Traditional OSCs with a nontransparent Al electrode fabricated by J52:IEICO‐4Cl, PBDB‐T:IEICO‐4Cl, and PTB7‐Th:IEICO‐4Cl yield power conversion efficiencies (PCE) of 9.65 ± 0.33%, 9.43 ± 0.13%, and 10.0 ± 0.2%, respectively. By using 15 nm Au as the electrode, semitransparent OSCs based on these three blends also show PCEs of 6.37%, 6.24%, and 6.97% with high average visible transmittance (AVT) of 35.1%, 35.7%, and 33.5%, respectively. Furthermore, via changing the thickness of Au in the OSCs, the relationship between the transmittance and efficiency is studied in detail, and an impressive PCE of 8.38% with an AVT of 25.7% is obtained, which is an outstanding value in the semitransparent OSCs.     

Ternary Nonfullerene Polymer Solar Cells with 12.16% Efficiency by Introducing One Acceptor with Cascading Energy Level and Complementary Absorption

A novel small‐molecule acceptor, (2,2′‐((5E,5′E)‐5,5′‐((5,5′‐(4,4,9,9‐tetrakis(5‐hexylthiophen‐2‐yl)‐4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl)bis(4‐(2‐ethylhexyl)thiophene‐5,2‐diyl))bis(methanylylidene)) bis(3‐hexyl‐4‐oxothiazolidine‐5,2‐diylidene))dimalononitrile (ITCN), end‐capped with electron‐deficient 2‐(3‐hexyl‐4‐oxothiazolidin‐2‐ylidene)malononitrile groups, is designed, synthesized, and used as the third component in fullerene‐free ternary polymer solar cells (PSCs). The cascaded energy‐level structure enabled by the newly designed acceptor is beneficial to the carrier transport and separation. Meanwhile, the three materials show a complementary absorption in the visible region, resulting in efficient light harvesting. Hence, the PBDB‐T:ITCN:IT‐M ternary PSCs possess a high short‐circuit current density (J_sc) under an optimal weight ratio of donors and acceptors. Moreover, the open‐circuit voltage (V_oc) of the ternary PSCs is enhanced with an increase of the third acceptor ITCN content, which is attributed to the higher lowest unoccupied molecular orbital energy level of ITCN than that of IT‐M, thus exhibits a higher V_oc in PBDB‐T:ITCN binary system. Ultimately, the ternary PSCs achieve a power conversion efficiency of 12.16%, which is higher than the PBDB‐T:ITM‐based PSCs (10.89%) and PBDB‐T:ITCN‐based ones (2.21%). This work provides an effective strategy to improve the photovoltaic performance of PSCs.     

Improved Efficiency and Stability of Perovskite Solar Cells Induced by CO Functionalized Hydrophobic Ammonium‐Based Additives

Because of the rapid rise of the efficiency, perovskite solar cells are currently considered as the most promising next‐generation photovoltaic technology. Much effort has been made to improve the efficiency and stability of perovskite solar cells. Here, it is demonstrated that the addition of a novel organic cation of 2‐(6‐bromo‐1,3‐dioxo‐1H‐benzo[de]isoquinolin‐2(3H)‐yl)ethan‐1‐ammonium iodide (2‐NAM), which has strong Lewis acid and base interaction (between C?O and Pb) with perovskite, can effectively increase crystalline grain size and reduce charge carrier recombination of the double cation FA_0.83MA_0.17PbI_2.51Br_0.49 perovskite film, thus boosting the efficiency from 17.1 ± 0.8% to 18.6 ± 0.9% for the 0.1 cm² cell and from 15.5 ± 0.5% to 16.5 ± 0.6% for the 1.0 cm² cell. The champion cell shows efficiencies of 20.0% and 17.6% with active areas of 0.1 and 1.0 cm², respectively. Moreover, the hysteresis behavior is suppressed and the stability is improved. The result provides a promising route to further elevate efficiency and stability of perovskite solar cells by the fine tuning of triple organic cations.