ZiQi Sun

Perovskite solar cells (PSCs) and organic solar cells (OSCs) are promising renewable light-harvesting technologies with high performance, but the utilization of hazardous dopants and high boiling additives is harmful to all forms of life and the environment. Herein, new multirole π-conjugated polymers (P1–P3) are developed via a rational design approach through theoretical hindsight, further successfully subjecting them into dopant-free PSCs as hole-transporting materials and additive-free OSCs as photoactive donors, respectively. Especially, P3-based PSCs and OSCs not only show high power conversion efficiencies of 17.28% and 8.26%, but also display an excellent ambient stability up to 30 d (for PSCs only), owing to their inherent superior optoelectronic properties in their pristine form. Overall, the rational approach promises to support the development of environmentally and economically sustainable PSCs and OSCs.

New multirole π-conjugated polymers are developed via a rational design approach through theoretical hindsight, further successfully subjecting them into dopant-free perovskite solar cells as hole-transporting materials with high power conversion efficiency (PCE) of 17.28%, and additive-free organic solar cells as photoactive donors with high PCE of 8.26%.

In article number 1601731, Xiao Cheng Zeng and co-workers report a theoretical study on single-layer hybrid perovskites semiconductors. The single-layer hybrid perovskites not only possess desired electronic properties for potential optoelectronic and photovoltaic applications, but also can achieve improved stability and functionalities through effective encapsulation and/or heterogeneously stacking with other two-dimensional materials.

Development of high-performance donor–acceptor (D–A) copolymers is vital in the research of polymer solar cells (PSCs). In this work, a low-bandgap D–A copolymer based on dithieno[3,2-b:2′,3′-d]pyridin-5(4H)-one unit (DTP), PDTP4TFBT, is developed and used as the donor material for PSCs with PC₇₁BM or ITIC as the acceptor. PDTP4TFBT:PC₇₁BM and PDTP4TFBT:ITIC solar cells give power conversion efficiencies (PCEs) up to 8.75% and 7.58%, respectively. 1,8-Diiodooctane affects film morphology and device performance for fullerene and nonfullerene solar cells. It inhibits the active materials from forming large domains and improves PCE for PDTP4TFBT:PC₇₁BM cells, while it promotes the aggregation and deteriorates performance for PDTP4TFBT:ITIC cells. The ternary-blend cells based on PDTP4TFBT:PC₇₁BM:ITIC (1:1.2:0.3) give a decent PCE of 9.20%.

A low-bandgap D–A copolymer based on dithieno[3,2-b:2′,3′-d]pyridin-5(4H)-one unit, PDTP4TFBT, is developed and used as the donor material for polymer solar cells. PDTP4TFBT is among a few D–A copolymers that can deliver >7% power conversion efficiencies (PCEs) in both fullerene and nonfullerene solar cells. Ternary-blend solar cells based on PDTP4TFBT, PC₇₁BM, and ITIC give a PCE of 9.20%.

Rubidium (Rb) is explored as an alternative cation to use in a novel multication method with the formamidinium/methylammonium/cesium (Cs) system to obtain 1.73 eV bangap perovskite cells with negligible hysteresis and steady state efficiency as high as 17.4%. The study shows the beneficial effect of Rb in improving the crystallinity and suppressing defect migration in the perovskite material. The light stability of the cells examined under continuous illumination of 12 h is improved upon the addition of Cs and Rb. After several cycles of 12 h light–dark, the cell retains 90% of its initial efficiency. In parallel, sputtered transparent conducting oxide thin films are developed to be used as both rear and front transparent contacts on quartz substrate with less than 5% parasitic absorption of near infrared wavelengths. Using these developments, semi-transparent perovskite cells are fabricated with steady state efficiency of up to 16.0% and excellent average transparency of ≈84% between 720 and 1100 nm. In a tandem configuration using a 23.9% silicon cell, 26.4% efficiency (10.4% from the silicon cell) in a mechanically stacked tandem configuration is demonstrated which is very close to the current record for a single junction silicon cell of 26.6%.

Rubidium doping improves the crystallinity and suppresses the defect migration in the 1.73 eV bandgap perovskite, which lead to improvement in cell performance and light stability. Semi-transparent perovskite cell with efficiency of 16% and average transparency of 84% between 720 and 1100 nm is fabricated. By combining with 23.9% silicon cell, efficiency of 26.4% for four terminal tandem is obtained.

In article number 1604695, Wallace C.H. Choy and co-workers propose a novel room-temperature scheme of pyridine-promoted formation of perovskite films featuring large grain-sizes, and high crystallinity, while being free of residues. This new approach enables the fabrication of all room-temperature, solution-processed perovskite solar cells (PVSCs) with a record efficiency of 17.10% and 14.19%, with no hysteresis on rigid and flexible substrate respectively.

Phototransistors with a structure of a nitrogen-doped graphene quantum dots (NGQDs)–perovskite composite layer and a mildly reduced graphene oxide (mrGO) layer are fabricated through a solution-processing method. This hybrid phototransistor exhibits broad detection range (from 365 to 940 nm), high photoresponsivity (1.92 × 10⁴ A W⁻¹), and rapid response to light on–off (≈10 ms). NGQDs offer an effective and fast path for electron transfer from the perovskite to the mrGO, resulting in the improvement of photocurrent and photoswitching characteristics. The high photoresponsivity can also be ascribed to a photogating effect in the device. In addition, the phototransistor shows good stability with poly(methyl methacrylate) encapsulation, and can maintain 85% of its initial performance for 20 d in ambient air.

A solution-processed phototransistor based on the composite of a perovskite modified by nitrogen-doped graphene quantum dots (NGQDs) and mildly reduced graphene oxide shows a high photoresponsivity of up to 1.92 × 10⁴ A W⁻¹, a broad photodetection range of UV–vis–NIR, and good stability in air.