# Overview on Different Types of Solar Cells: An Update
## 2 Organic Solar Cells
### Efficiency Highlights
A high PCE of 15% along with a V\({}_{\rm oc}\) of 1.59 V, I\({}_{\rm sc}\) of 13.3 mA/cm\({}^{2}\), and fill factor of 0.71 were achieved. The effect of regioregularity of the backbone and the fused-ring core modulation of the polymer acceptor on the performance of OSC was demonstrated by [PERSON] and co-workers [105]. The OSC was fabricated using PBDB-T as the donor with a new class of polymeric acceptor benzotriazole (BTz)-core fused-ring segment. A maximum PCE of 15.8% was achieved for the regioregular acceptor (PZT-\(\gamma\))-based OSC in addition to an enhanced I\({}_{\rm sc}\), V\({}_{\rm OC}\), and FF of 24.7 mA/cm\({}^{2}\), 0.896 V, and 0.71, respectively. The application of a novel polymer acceptor, PYT-1S1 Se, an asymmetrical selenophene-fused backbone, while using Poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo [1,2-b:4,5-b']dithiorene))-alt-(5,5-(1',3'-di-2-thienylyl-5,7'-bis(2-ethylhexyl)benzo [1',2'-c:4',5'-c']dithiiophene-4,8-dione)] (PBDB-TF) as the donor polymer was able to achieve a high PCE, V\({}_{\rm OC}\), I\({}_{\rm SC}\), and FF of 16.3%, 0.926 V, 24.1 mA/cm\({}^{2}\), and 0.73, respectively [106]. The development of novel polymeric acceptors by polymerizing an efficient small-molecule acceptor, 2,2'-((2Z,2'Z)-((12,13-bis(2-ethylhexyl)-3,9-(2-butyloctyl)-12,13-dihydro-[1,2,5]thiadiazol [3,4-e]thieno [2\",3\":4',5]thieno [2',3':4,5]pyrro [3,2-g]thieno [2',3':4,5]thieno [3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (L8-BO) and its subsequent OSC device manufacturing with PBDB-TF as the donor, was demonstrated by [PERSON] and co-workers [107]. The fabricated all polymer-OSC devices achieved a \(\mathrm{V_{oc}}\) of 0.949 V, \(\mathrm{J_{Sc}}\) of 23.73 mA/cm\({}^{2}\), FF of 0.74, and PCE of 16.76%. An effective strategy for improvement in the performance of OSC is additive engineering. However, only limited concentrations of traditional additives can be incorporated, such as 1,8-diiodooctane (DIO) or 1-chloronaphthalene (CN) along with an induced lower stability. Moreover, additional thermal treatment is required, which is an obvious hurdle for industrial applications. In this context, 1,3-diiodobenzene (1,3-DIB) has proved to be a versatile and effective solid additive [108]. A NFA thiadiazolo [3,4-e]thieno [2\",30':4',50]thieno [20,30:4,5]pyrrolo [3,2-g]thieno [20,30:4,5]thieno [3,2-b]indole-2,10-diyl)bis(methanyylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)) dimalononitrile (Y6) has gained considerable interest recently. The incorporation of 1,3-DIB in PBD-TF:Y6 resulted in an improvement in Voc, Jsc, FF, and PCE from 0.87 V, 25.08 mA/cm\({}^{2}\), 0.71, and 15.36% to 0.85 V, 26.0 mA/cm\({}^{2}\), 0.76, and 16.90%, respectively. All-polymer OSCs have gained significant attention recently. A ternary-all-polymer OSC composed of PBD-TF as the donor along with a combination of poly[(2,2'-(2,2'Z')-((12,13-bis(2-octyldodecyl)-3,9-diundecyl-12,13-hydrox [1,2])thiazolo [3,4e]thieno [2\",3\":4',5']thieno [2\",3\":4',5']]thieno [2',3':4',5']pyrrolo [3,2-g]thieno [2',3':4,5]thieno [2',3':4,5]thieno [3,2-b]-indole-2,1'-diyl)bis(methanyylidene)bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile-alt-2,5-thiophene)] (PYT) and a novel fluorinated polymer named PY2F-T as the acceptor had \(\mathrm{V_{oc}}\), \(\mathrm{I_{sc}}\), FF, and PCE of 0.90 V, 25.2 mA/cm\({}^{2}\), 0.76, and 17.2%, respectively. A new donor-acceptor polymer where donor D18 was connected to a fused ring acceptor DTBT was proposed for the improvement of the OSC performance [109]. The single-junction OSC based on D18:Y6 demonstrated a PCE of 18.22% owing to its high hole mobility and wide band gap of D18. The improvement in the performance by the incorporation of additives has gained considerable interest. Two volatile solid additives (SADs) are designed according to their conformation; SAD1 is a twisted-type while SAD2 is a planar-type [110].