wangzhaowei

Five polymer donors with distinct chemical structures and different electronic properties are surveyed in a planar and narrow-bandgap fused-ring electron acceptor (IDIC)-based organic solar cells, which exhibit power conversion efficiencies of up to 11%.

The selectivity of electrodes of solar cells is a critical factor that can limit the overall efficiency. If the selectivity of an electrode is not sufficient both electrons and holes recombine at its surface. In materials with poor transport properties such as in organic solar cells, these surface recombination currents are accompanied by large gradients of the quasi-Fermi energies as the driving force. Experimental results from current–voltage characteristics, advanced photo- and electroluminescence as well as charge extraction of three different photoactive materials are shown and compared to drift-diffusion simulations. It can be concluded that in cases of electrodes with reduced selectivity the decrease of the open-circuit voltage can be divided into two distinct contributions, the reduction of the overall steady-state charge carrier density and the gradients of the quasi-Fermi energies. The results clearly show that for photoactive layers with poor transport properties, the gradient of the quasi-Fermi energy in the vicinity of the contact is the main contribution to the loss in open-circuit voltage. For imbalanced mobilities, this gives rise to the phenomenon that it is more challenging to realize a selective contact for the less mobile charge carrier, i.e., the hole contact in most organic solar cells.

The impact of charge carrier mobility and electrode selectivity on surface recombination is investigated by drift-diffusion modeling, charge extraction, electro- and photoluminescence. It is shown that for organic solar cells the reduced open-circuit voltage is not only due to actual recombination of charge carriers at the contact but mainly a consequence of the required driving force for the majority carriers.

In addition to a good perovskite light absorbing layer, the hole and electron transport layers play a crucial role in achieving high-efficiency perovskite solar cells. Here, a simple, one-step, solution-based method is introduced for fabricating high quality indium-doped titanium oxide electron transport layers. It is shown that indium-doping improves both the conductivity of the transport layer and the band alignment at the ETL/perovskite interface compared to pure TiO₂, boosting the fill-factor and voltage of perovskite cells. Using the optimized transport layers, a high steady-state efficiency of 17.9% for CH₃NH₃PbI₃-based cells and 19.3% for Cs_0.05(MA_0.17FA_0.83)_0.95Pb(I_0.83Br_0.17)₃-based cells is demonstrated, corresponding to absolute efficiency gains of 4.4% and 1.2% respectively compared to TiO₂-based control cells. In addition, a steady-state efficiency of 16.6% for a semi-transparent cell is reported and it is used to achieve a four-terminal perovskite-silicon tandem cell with a steady-state efficiency of 24.5%.

Solution-processed, indium-doped TiO_x films are shown to be very effective electron transport/hole-blocking layers for high-performance perovskite cells. Doping improves the conductivity and work-function energy alignment at the ETL/perovskite interface, leading to high fill-factor and open-circuit voltage. An efficiency of ≈19.3% is demonstrated for a perovskite cell, and a steady-state efficiency of 24.5% is presented for a four-terminal perovskite-silicon tandem cell.

On page 9204, thinness-controllable ultrathin perovskite wafers are prepared by Z. Yang, S. Z. (F.) Liu, and co-workers using a microreactor. Based on the single-crystalline perovskite wafer, high-performance photoresponse arrays are fabricated, demonstrating the feasibility of mass production of integrated circuits (ICs) on the perovskite wafer. It is envisioned that the present technique may provide an effective strategy for single-crystalline wafer preparation for demanding high-quality, low-cost device applications.

Ternary polymer solar cells are fabricated based on one donor PBDB-T and two acceptors (a methyl-modified small-molecular acceptor (IT-M) and a bis-adduct of Bis[70]PCBM). A high power conversion efficiency of 12.2% can be achieved. The photovoltaic performance of the ternary polymer solar cells is not sensitive to the composition of the blend.

A robust and efficient interconnection layer (ICL) based on low conductive poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) and ZnO nanoparticles is implemented in a solution-air-processed, blade coated inverted polymer tandem solar cell. The commercial PEDOT:PSS (Heraeus Clevios P VP Al 4083) is modified with a fluorosurfactant to allow its deposition onto any hydrophobic active layer surface. However, this method alters the electrical and energetic properties of the PEDOT:PSS thus affecting the interface with the ZnO layer, responsible for an inefficient ICL and poorly performing tandem devices. The ohmic contact at the PEDOT:PSS/ZnO interface is successfully optimized through a simple solvent treatment of the PEDOT:PSS film surface, leading to tandem devices with power conversion efficiencies (PCEs) improved by more than 50% compared to the untreated reference system. The reported method is an easy and versatile approach to optimize the functionality of the PEDOT:PSS/ZnO ICL of inverted multijunction devices, applicable onto any organic active layer and compatible with a roll-to-roll production line.

Air processed inverted tandem solar cells are fabricated using surfactant modified poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) and ZnO as interconnection layer (ICL). Limitations at the PEDOT:PSS/ZnO interface, induced by the presence of surfactant in the PEDOT:PSS film, are solved by solvent-treating the surface of the PEDOT:PSS layer. This results a versatile and scalable approach for processing the ICL of organic multijunction devices.

Organic–inorganic hybrid perovskite solar cells have undergone an unprecedented development as the next-generation photovoltaic devices in recent years. The power conversion efficiency and stability are the key factors attracting great attentions from both academic and industrial communities. Here, a nonoxide CdS layer is inserted between TiO₂ and perovskite to passivate the TiO₂ interface in planar-type perovskite solar cells. After introducing the CdS layer, significantly enhanced air stability and suppressed recombination between the trapped electrons and perovskite related to inverse transport are observed. At the optimum CdS thickness, a champion power conversion efficiency of 14.26% is achieved compared with 10.31% for the reference CdS-free devices. This impressive efficiency also surpasses that of previously reported perovskite solar cells based on CdS. The largely improved performance is ascribed to the increased Fermi level of the electron transport layer, more efficient charge transport, and lower recombination rates.

Insertion of a CdS layer between TiO₂ and perovskite passivates the defects at the TiO₂ surface, extracts electrons from perovskite more efficiently, reducing recombination at the interface of TiO₂/perovskite, resulting in improved conversion efficiencies and air stability of perovskite solar cells.

Simple organic salts are used as a cheap alternative for hole-conducting materials in methylammonium lead bromide perovskite solar cells and obtaining power conversion efficiency of 4.4%. The findings suggest that the polar organic salts interact with the perovskite surface, leading to formation of a surface dipole or change of an existing one on the perovskites that changes its effective work function.

The extent to which the soft structural properties of metal halide perovskites affect their optoelectronic properties is unclear. X-ray diffraction and micro-photoluminescence measurements are used to show that there is a coexistence of both tetragonal and orthorhombic phases through the low-temperature phase transition, and that cycling through this transition can lead to structural changes and enhanced optoelectronic properties.