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%.

Obtaining both high open-circuit voltage (Voc) and short-circuit current density (Jsc) has been a major challenge for efficient all-polymer solar cells (all-PSCs). Herein, we developed a polymer acceptor PF5-Y5 with...

We present a non-fullerene electron acceptor bearing a fused 10-heterocyclic ring with a narrow band gap, which achieved a power conversion efficiency of 6.5% when paired with PTB7-Th.

Charge transport in organic photovoltaic (OPV) devices is often characterized by space-charge limited currents (SCLC). However, this technique only probes the transport of charges residing at quasi-equilibrium energies in the disorderbroadened density of states (DOS). In contrast, in an operating OPV device the photogenerated carriers are typically created at higher energies in the DOS, followed by slow thermalization. Here, by ultrafast time-resolved experiments and simulations it is shown that in disordered polymer/fullerene and polymer/polymer OPVs, the mobility of photogenerated carriers significantly exceeds that of injected carriers probed by SCLC. Time-resolved charge transport in a polymer/polymer OPV device is measured with exceptionally high (picosecond) time resolution. The essential physics that SCLC fails to capture is that of photo generated carrier thermalization, which boosts carrier mobility. It is predicted that only for materials with a sufficiently low energetic disorder, thermalization effects on carrier transport can be neglected. For a typical device thickness of 100 nm, the limiting energetic disorder is σ ≈71 (56) meV for maximum-power point (short-circuit) conditions, depending on the error one is willing to accept. As in typical OPV materials the disorder is usually larger, the results question the validity of the SCLC method to describe operating OPVs.

All-polymer organic solar cells offer exceptional stability. Unfortunately, the use of bulk heterojunction (BHJ) structure has the intrinsic challenge to control the side-chain entanglement and backbone orientation to achieve sophisticated phase separation in all-polymer blend. Here, we revealed that the P-iN structure can outperform the BHJ ones with a nearly 50% efficiency improvement, reaching a power conversion efficiency approaching 10%. This P-iN structure can also provide enhanced internal electric field and remarkably stable morphology under harsh thermal stress. We have further demonstrated generality of the P-iN structure in several other all-polymer systems. Considering the adjustable polymer molecular weight and solubility, the PiN device structure can be more beneficial for all-polymer systems. With the design of more crystalline polymers, the antiquated P-iN structure can further show its strength in all-polymer system by simplified morphology control and improved carrier extraction, becoming a more favorite device structure than dominant BHJ structure.

Thermal annealing on TQ1:N2200 all-polymer solar cells leads to higher photocurrent, fill factor, and almost doubled efficiency. Current maps from conductive-AFM are shown.

still far behind those of inorganic counterparts, such as sc-Si, GaAs, CdTe, CIGS, and Perovskite solar cells. [ 2 ] One of the main reasons is their low open-circuit voltage ( V oc ) due to the large energy loss per absorbed photon. The minimum energy loss ( E loss ) is defi ned by the equation: E loss = E g − qV oc , where E g is the optical gap of the main light absorber, in most cases the donor material. Decreasing E loss will enhance the V oc and thus PCEs of PSCs. [3][4][5] The minimum E loss for efficient charge generation in organic solar cells (OSCs) is suggested to be 0.6 eV, [ 6 ] and E loss below 0.6 eV often leads to ineffi cient charge generation and low quantum effi ciency, limiting the photocurrent and PCEs. [ 7 ] Typically, the E loss for polymer:fullerene based PSCs with high PCEs of 9%−11% is between 0.7 and 0.9 eV. [8][9][10] In contrast, Perovskite solar cells have a high V oc (> 1 V) with E loss of ≈0.5 eV, which partially accounts for their much higher PCEs of ≈20%. [ 11,12 ] The E loss values for inorganic solar cells, such as sc-Si, GaAs, GaInP, CdTe, CIGS-based solar cells are normally between 0.3 and 0.6 eV. [ 13 ] In Figure 1 and Table S1 in the Supporting Information, we summarize a selection of solar cells exhibiting either One of the factors limiting the performance of organic solar cells (OSCs)is their large energy losses ( E loss ) in the conversion from photons to electrons, typically believed to be around 0.6 eV and often higher than those of inorganic solar cells. In this work, a novel low band gap polymer PIDTT-TID with a optical gap of 1.49 eV is synthesized and used as the donor combined with PC 71 BM in solar cells. These solar cells attain a good power conversion effi ciency of 6.7% with a high open-circuit voltage of 1.0 V, leading to the E loss as low as 0.49 eV. A systematic study indicates that the driving force in this donor and acceptor system is suffi cient for charge generation with the low E loss . This work pushes the minimal E loss of OSCs down to 0.49 eV, approaching the values of some inorganic and hybrid solar cells. It indicates the potential for further enhancement of the performance of OSCs by improving their V oc since the E loss can be minimized.

The considerable improvement on the power conversion efficiency (PCE) for emerging nonfullerene polymer solar cells is still limited by considerable voltage losses that have become one of the most significant obstacles infurther boosting desired photovoltaic performance. Here, a comprehensive study is reported to understand the impacts of charge transport, energetic disorder, and charge transfer states (CTS) on the losses in open-circuit voltage (V oc ) based on three high performing bulk heterojunction solar cells with the best PCE exceeding 11%. It is found that the champion poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)-benzo[1,2-c:4,5-c′]dithiophene-4,8-dione))] (PBDB-T):IT-M solar cell (PCE = 11.5%) is associated with the least disorder.The determined energetic disorder in part reconciles the difference in V oc between the solar cells. A reduction is observed in the nonradiative losses (ΔV nonrad ) coupled with the increase of energy of CTS for the PBDB-T:IT-M device, which may be related to the improved balance in carrier mobilities, and partially can explain the gain in V oc . The determined radiative limit for V oc combined with the ΔV nonrad generates an excellent agreement for the V oc with the experimental values. The results suggest that minimizing the energetic disorder related to transport and CTS is critical for the mitigation of V oc losses and improvements on the device performance.