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The development of narrow bandgap A-D-A- and ADA'DA-type non-fullerene small molecule acceptors (NFSMAs) along with small molecule donors (SMDs) have led to significant progress in all-small molecule organic solar cells. Remarkable power conversion efficiencies, nearing the range of 17-18 %, have been realized. These efficiency values are on par with those achieved in OSCs based on polymeric donors. The commercial application of organic photovoltaic technology requires the design of more efficient organic conjugated small molecule donors and acceptors. In recent years the precise tuning of optoelectronic properties in small molecule donors and acceptors has attracted considerable attention and has contributed greatly to the advancement of all-SM-OSCs. Several reviews have been published in this field, but the focus of this review concerns the advances in research on OSCs using SMDs and NFSMAs from 2018 to the present. The review covers the progress made in binary and ternary OSCs, the effects of solid additives on the performance of all-SM-OSCs, and the recently developed layer-by-layer deposition method for these OSCs. Finally, we present our perspectives and a concise outlook on further advances in all-SM-OSCs for their commercial application., (© 2024 Wiley-VCH GmbH.)

A new wide-bandgap conjugated D-A polymer denoted as P106 with a medium acceptor dithieno [2,3-e;3'2'-g]isoindole-7,9 (8H) (DTID) unit and strong 2-dodecylbenzo[1,2-b:3,4-b':6,5-b"]trithiophene (3TB) donor units shows an optical bandgap of 2.04 and highest occupied molecular orbital energy level of -5.56 eV. P106 is used as the donor and two nonfullerene acceptors-medium bandgap DBTBT-IC and narrow band Y18-DMO-are used as acceptors for the construction of binary and ternary bulk heterojunction polymer solar cells. The optimized polymer solar cells based on P106 : DBTBT-IC and P106 : Y18-DMO exhibit power conversion efficiencies of 11.76 % and 14.07 %, respectively. The short-circuit current density (22.78 mA cm -2 ) for the P106 : Y18-DMO device is higher than that for P106 : DBTBT-IC (18.56 mA cm -2 ) one, which could be attributed to the more photon harvesting efficiency of the P106 : Y18-DMO active layer. In light of the high short-circuit current densities and fill factors for the Y18-DMO based device and the high value of open circuit voltage of the DBTBT-IC based device, ternary polymer solar cells are fabricated by using ternary active layer (P106 : DBTBT-IC : Y18-DMO) and achieve a power conversion efficiency of 16.49 % with low energy loss of 0.47 eV., (© 2021 Wiley-VCH GmbH.)

The effect of central donor core on the properties of A-π-D-π-A donors, where D is a porphyrin macrocycle, cyclopenta[2,1-b:3,4-b']dithiophene is the π bridge, and A is a dicyanorhodanine terminal unit, was investigated for the fabrication of the organic solar cells (OSCs), along [6,6]-phenyl-C71-butyric acid methyl ester (PC 71 BM) as electron acceptor. A new molecule consisting of Ni-porphyrin central donor core (VC9) showed deep HOMO energy level and OSCs based on optimized VC9:PC 71 BM realized overall power conversion efficiency (PCE) of 10.66 % [short-circuit current density (J SC )=15.48 mA/cm 2 , fill factor (FF)=0.65] with high open circuit voltage (V OC ) of 1.06 V and very low energy loss of 0.49 eV, whereas the Zn-porphyrin analogue VC8:PC 71 BM showed PCE of 9.69 % with V OC of 0.89 V, J SC of 16.25 mA/cm 2 and FF of 0.67. Although the OSCs based on VC8 showed higher J SC in comparison to VC9, originating from the broader absorption profile of VC8 that led to more exciton generation, the higher value of PCE of VC9 is owing to the higher V OC and reduced energy loss., (© 2020 Wiley-VCH GmbH.)